ATTACHMENT E: MINERALS

This attachment covers industrial processing of non-metallic minerals, including the categories listed below. Emissions from fuel combustion processes that are associated with the production of non-metallic mineral categories are assigned to the last two listed categories.

Description EIC Code CES NumberSand & Gravel Excavation and Processing 430-422-7078-0000 46995 Grinding/Crushing of Aggregates 430-426-7078-0000 47019 Cement Concrete Production 430-430-7018-0000 47035 Asphaltic Concrete Production 430-424-7006-0000 47001 Surface Blasting 430-428-7000-0000 47027 Industrial Distillate Oil Combustion 050-995-1220-0000 66803 Industrial Natural Gas Combustion (Unspecified) 050-995-0110-0000 47124

SAND AND GRAVEL EXCAVATION AND PROCESSING

Differing processes produce two types of sand and gravel: construction and industrial. Construction sand and gravel, which are used for construction projects, are washed and sized to generate materials suitable for mixing with binders for asphalt or cement production. Industrial sand requires additional processing for use in glass products, ceramics, filters for rubber and plastics, and abrasive sand-blast media. Sand and gravel processes primarily include sizing, screening, transferring mineral products, and loading/unloading (Hayden, pers. comm., 2001). Additional processes include washing, drying, and some crushing. The US Environmental Protection Agency (EPA) document, Compilation of Air Pollutant Emission Factors (AP-42), provides emissions estimation guidance for sand and gravel production processes. EPA recommends different emissions estimation methods for the production and handling of gravel, construction sand, and industrial sand.

Sand and Gravel Process Overview and Associated Emissions

Construction Sand And Gravel Facilities

A sand or gravel plant normally has multiple emissions sources of the same type, such as transfer points. Appropriate emission factors must be applied for each emissions point. For this guidance memorandum, we have formulated process diagrams for typical sand and gravel plants on the basis of reference materials and the advice of staff members from several industry associations (Falasco, pers. comm., 2001; Hayden, pers. comm., 2001; EPA, 1996; National Stone Association, 1995). Figure 1 depicts the process diagram for a construction sand and gravel plant. Fugitive emissions from truck loading and unloading are modeled as batch drop rather than continuous conveyor drop processes. Material is generally transported by trucks four times: once to transport material from the excavation site to storage areas, again from the stockpiles to begin processing, a third time from the processing site to product storage areas, and finally to move the material from storage piles to the point of sale. When needed, continuous

1

conveyer drops are employed to deposit materials onto storage piles. Information from AP-42 suggests that there may be at least three conveyor transfer points, which correlates with information discussed with an industry contact (Young, pers. comm., 2001). In addition to fugitive emission sources, Figure 1 illustrates process emissions. Initially, a screening process separates oversized gravel from finer sand and gravel. A second screen separates gravel from fine sand. Construction sand usually is screened only twice, while gravel normally is screened several times (depending on its initial grade). Oversized gravel, or gravel that does not fit through the screen, typically is crushed and re-screened up to three times. Figure 1 indicates the fractional proportions of the initial aggregate gravel that typically must be crushed and re-screened at each of the three screening stages. In the final sand classification stage, sand is sized through a wet process, which eliminates silt and other impurities. It is assumed that wet classification raises negligible PM emissions.

AP-42 provides the emission factors listed in Table 1 to estimate PM and PM10 emissions for various sand and gravel production processes. These emission factors, which represent dry conditions, should be considered to reflect worst case conditions. This is because sand and gravel materials are often moist when handled and thus raise negligible dust.

Table 1. PM and PM10 emission factors for crushed aggregate processing plants (EPA, 1996; EPA, 1995a; National Stone Association, 1995).

Process PM10 (lb/ton) PM (lb/ton) a

Uncontrolled conveyor transfer point 0.0014 NABatch drop of bulk loading 0.0024 0.24Continuous drop, pile formation 0.06 NATruck loading by conveyor 0.00010 NATruck unloading of fragmented stone 0.000016 NAUncontrolled screening 0.015 NAUncontrolled crushing (upper-limit estimation) 0.0024 0.036Uncontrolled storage piles 0.020 0.043

a NA indicates that the data is not available. When emission factors for total PM10 are not available those for PM are used.

The emission factor for storage piles that is shown in Table 1 was derived from an AP-42 equation, shown below (EPA, 1995a).

where:EF = PM10 emission factor in units of pounds per ton of sand or gravelk = Aerodynamic particle size multiplier (0.35 for PM10 and 0.74 for PM) U = Mean wind speed (miles per hour)

M = Material moisture content (% of total mass)

2

Primary Crusher

Crush(1&2)

StoragePiles

Wet Material

Drill/Dredge

TruckUnload

StoragePiles

Wet Drilling

TruckUnload

Batch Drop (1)

Screen (1)

CTP (2)

ConveyorTransferPoint (CTP) (1)

ConveyorTransfer Point(CTP) (2)

25% + 1%

100%

1st Screen

Conveyor

ConstructionSand =50%

CTP (3)

Conveyor

2nd Screen

Screen (2)

ContinuousDrop

StoragePiles

ContinuousDrop (2)

BatchDrop (2)

TruckUnload100%

Batch Drop (3)StoragePiles

Pointof Sale

TruckUnload

Storage Piles

100%

ContinuousDrop

ConstructionGravel =50%Washing/

Scrubbing

Wet Classifying

Dewatering

CTP (4)

ConstructionSand =50%

StoragePiles

Figure 1. Process diagram for a typical construction sand and gravel manufacturing facility.

3

Generally, moisture content is between 1.5 and 4% (Falasco, pers. comm., 2001). However, in arid climates or during hotter times of year, material may dry more quickly. For the emissions estimates presented in this attachment, input variables were selected to estimate conservatively high emissions. A wind speed of 15 mph was assumed as a reasonable upper limit for worst-case conditions, and the recommended default moisture content of 0.7% was applied. If local meteorological data or moisture contents are available then more accurate emission factors can be developed to update these estimates.

Industrial Sand Facilities

Industrial sand is mined from deposits of silicate rock or quartz-rich sand or sandstone. Initially, the processing stages are very similar to those for construction sand and gravel. However, industrial sand undergoes additional processing steps due to differences in final product requirements and raw material extraction processes (see process diagram, Figure 2). The mining process for industrial sand includes drilling and occasional blasting to loosen large deposits. In addition, industrial sand needs extra processing to meet the more stringent requirements of the glass manufacturing, plastic filter manufacturing, and abrasive-blasting industries. For fine, high-quality sand that is free from impurities such as clay or other minerals, even further processing steps are necessary, such as grinding, scrubbing, and drying. After grinding, sizing, and scrubbing, the sand is dried with a rotary dryer and is classified by size for sale. During these last processing stages, industrial sand has a lower moisture content than that of construction sand.

EPA (1996) and the National Stone Association (1995) recommend the emission factors listed in Table 2 for screening, handling, transfer, and storage of low-moisture, fine sands. In addition, emissions from the process of drying itself should be considered. Typically, dryers are natural gas- or diesel-powered sources of combustion by-products.

Table 2. Emission factors for industrial sand plants (EPA, 1996; EPA, 1998a; National Stone Association, 1995).

ProcessEmission Factorsa

(lb/ton) PollutantFines crushing 0.072 PM

0.015 PM10

Industrial sand handling, transfer and storage with wet scrubber

0.00130.0013

PMPM10

Sand screening with a Venturi scrubber 0.0083 PM0.0021 PM10

Sand dryer with wet scrubberb 0.039 PM0.031 NOx

0.0189 CO0.00124 VOC

0.000135 SOxaEmission factor units are expressed in terms of pounds of pollutant emitted per ton of sand processed.bThe emissions from sand drying are attributed to the “Industrial Natural Gas Combustion (Unspecified)” emissions category.

4

UnloadingFragments

Drilling/Blast

TruckUnload

Storage PilesWet drilling

TruckUnload Batch Drop (1)

Screen (1)

CTP (3)

ConveyorTransferPoint (CTP) (1)

ConveyorTransfer Point(CTP) (2)

75% + 15%

Primary Crusher

Crush(1&2)

100%

1st Screen

Conveyor

Sand 100%CTP (4)

2nd Screen

Screen (2)

ContinuousDrop

StoragePiles

100%

ContinuousDrop

Ground Material Storagefor Construction Sand

StoragePiles

Organic and CombustionProcess Emissions

ContinuousDrop (2)

BatchDrop (2)

Batch drop (3)

Storage Piles

TruckUnload

StoragePiles

Pointof Sale

100%

TruckUnload

Wet Processing

Conveyor

Storage Piles

CTP (5)

Washing, WetClassifying,Scrubbing, andDesliming

Froth Floatation

Draining,Drying

3rd Screen

Sand dryer

CTP (6)

Grinding

Fines Crushing

100%

ControlledFines Screen

Figure 2. Process diagram for a typical industrial sand manufacturing facility.

5

The use of control technologies, such as Venturi scrubbers and wet scrubbers, was assumed. It is highly likely that industrial sand plants employ some type of control technology. If individual counties or air districts undertake a bottom-up approach to this category in the future, it would be helpful to ascertain the actual in-use control technologies and their control efficiencies.

Activity Data

The US Geological Survey (USGS), in cooperation with the California Department of Conservation, published estimated 1999 statewide productions of construction sand and gravel and industrial sand (USGS, 2001a). Production of aggregates, such as sand and gravel, is done only on a contract basis and is therefore sensitive to market fluctuations. While economic growth from 1999 to 2000 was significant for California’s nonmetallic minerals and construction industries (from 0.1 to 7% growth) (California Employment Development Department, 2001), this should introduce only a relatively small error in the emissions estimates (much less than 10%). Therefore, 1999 and 2000 estimated productions are assumed to be equal.

Construction sand and gravel production was estimated to be 150,000,000 metric tons, which is equal to 165,375,000 tons

Industrial sand production was estimated to be 1,820,000 metric tons, which is equivalent to 2,006,550 tons

The US Census Bureau “County Business Patterns” database provides county-level employment data for the sand and gravel industry (US Census Bureau, 2001), which were used to disaggregate statewide production of sand and gravel and estimate county-level productions. Data for North American Industry Classification System (NAICS) code numbers 212321 (Construction Sand and Gravel Mining) and 212322 (Industrial Sand Mining) were acquired.

Temporal Allocation

A seasonal pattern for sand and gravel processing emissions, shown below, was derived from a USGS report of quarterly sand and gravel sales in California (USGS, 2001b). The quarterly proportions for 1999 and 2000 were averaged to estimate this seasonal pattern. The USGS data includes both industrial and construction sand and gravel categories.

January through March, 18.8% April through June, 25.6% July through September, 28.1% October through December, 27.6%

The seasonal variability in sand and gravel extraction and processing is likely linked to road paving and construction. Regulations that restrict excavation from rivers during fish spawning season, which is during the spring, may also influence the seasonal variability. This

6

mandated production decrease most likely is already evident in the seasonal variation specified above; however, its impact on regions and counties will vary geographically.

A weekly and diurnal pattern, 12 hours per day and six days per week (Sundays off), is based on conversations with staff members of the National Stone, Sand, and Gravel Association (Hayden, per. comm., 2001). There are no standard hours of operation in this industry; the actual working periods vary by local, regional, and state regulations.

Additional Considerations

The National Stone Association (1995) suggests that the emission factors presented in Tables 1 and 2 represent worst-case conditions. The emission factors are from uncontrolled sources and without wet suppression of materials. Most plants employ wet suppression techniques in addition to other control technologies, such as baghouses, scrubbers on crushers, and covered transfer points. EPA suggests that dust suppression with water may reduce emissions by 70 to 95% (EPA, 1995a). Baghouses and scrubbers generally are rated to remove more than 99% of particulate matter from the vented stream.

A source of uncertainty is that particulate emissions from sand and gravel facilities vary considerably with the content of silt in the raw material (Lee C.H. et al, 2001). Silt is very fine PM of less then 75 micrometers in diameter. The higher the silt content of the raw material, the greater is the potential for particulate emissions; however, silt content is site specific and could not be addressed in this memorandum.

Vehicle traffic at sand and gravel facilities generates PM emissions due to wind erosion of silt from the road surface. The emissions from unpaved roads (CES No. 82156, EIC No. 645-648-5400-0000) can be estimated by using AP-42 emission factors from Chapter 13.2.2 Unpaved Roads. However, it is tricky to estimate the needed activity parameter, vehicle-miles of travel.

An addendum to this attachment, “Aggregate Fugitive And Process Emissions Inventory Guidelines” by the National Stone Association, is included as additional guidance to estimate bottom-up emissions for crushed stone, sand, and gravel plants. This guidance, which was prepared by the National Stone Association for permitting purposes, requires detailed facility-specific data and regional weather information.

For emissions from fugitive sources, low moisture content and windy conditions greatly increase emissions. Therefore, site-specific data are needed to incorporate these variables into emissions estimates.

Example Calculation for Sand and Gravel Processing

County-level sand and gravel production, which is difficult to obtain directly, is estimated by disaggregating statewide production to each county. The statewide production is apportioned according to the county-by-county distribution of employment in the Construction Sand and

7

Gravel Mining Sector, which the US Census Bureau identifies with the NAICS code no. 212321. For each of California’s counties, the Census Bureau either reports an exact number of employees or a range. If a range is given, the midpoint is used to quantify the proportion of statewide production assigned to a county.

Construction Gravel Processing Emissions

Below are example calculations for PM10 emissions from construction gravel production in Amador County. The Census Bureau reports that there is one construction sand and gravel processing facility in Amador County with zero to four employees (US Census Bureau, 2001), the midpoint of which is equal to two employees. The number of employees per county is divided by the total number of employees for the state to derive the proportion of state production.

2 employees (Amador) ÷ 3,106.5 total employees (California) = 0.00064

This proportion is multiplied by the state production to estimate the production of construction sand and gravel in Amador County.

0.0006 165,375,000 tons = 106,470 tons of construction sand and gravel

Industry professionals roughly estimate that the split between construction sand and gravel production is 50%/50% for the industry as a whole (Falasco, pers. comm., 2001). This is likely to vary by county, but it is the best information available at present.

106,470 tons 50% = 53,235 tons of construction gravel

The PM10 emissions from primary and secondary crushing of construction gravel are calculated by multiplying production by the corresponding emission factors (see Table 1). Only 25% of produced construction gravel typically is routed through primary crushing and 1% is routed through secondary crushing (see Figure 1).

53,235 tons 0.0024 lb/ton (25% + 1%) = 33 pounds PM10 = 0.017 tons PM10

PM10 emissions from primary, secondary, and tertiary screening are calculated similarly. Typically, a processing plant routes 100%, 25%, and 1% (respectively) of produced gravel through these processes. Lastly, 100% of material is graded (or sized) through a final screening step.

53,235 tons 0.015 lb/ton (100% + 25% + 1% + 100%) = 1,804 pounds PM10

= 0.90 tons PM10

Fugitive emission sources for a typical plant include three conveyor transfer points, three truck batch drops, one continuous drop by conveyor to form a pile, and storage of materials (as shown in Figure 1). Emission factors for these activities, which are listed in Table 1, are proportioned

8

according to the counts of similar emissions points at a typical facility (e.g., 3 batch drops, 1 conveyer drop, etc.).

53,235 tons [(3 0.0014) + (3 0.0024) + 0.06 +0.02] lb/ton = 4,870 pounds PM10

= 2.4 tons PM10

Total PM10 emissions for the processing of construction gravel are estimated as the sum of the emissions from crushing, screening, and fugitive sources.

33 + 1804 + 4870 = 6707 pounds = 3.4 tons PM10

Table 3 lists the results of similar calculations for all California counties that produce construction gravel. (These emissions should be reduced by reasonable control efficiencies if wet handling is known to occur.)

Construction Sand Processing Emissions

Production of construction sand for Amador County was calculated to be 53,235 tons (similar to the calculation above for construction gravel). Sand is screened twice to separate it from courser rocks and gravel. The final sand sizing stage, which eliminates silt and other impurities, is a wet process that produces negligible emissions. The emission factor for aggregate screening (see Table 1) was applied to estimate PM10 emissions due to screening processes.

53,235 tons (2 0.015) lb/ton = 1,597 pounds PM10 = 0.80 tons PM10

Fugitive PM10 emission sources include four conveyor transfer points, three truck batch drops, two continuous drops by conveyor to form a pile, and storage of materials (as seen in Figure 1). Emission factors for these activities, which are listed in Table 1, are proportioned according to the counts of similar emissions points at a typical facility (e.g., 3 batch drops, 2 conveyer drops, etc.).

53,235 tons [(4 0.0014) + (3 0.0024) + (2 0.06) + 0.02] lb/ton = 8,134 pounds PM10

= 4.1 tons PM10

Total PM10 emissions for the processing of construction sand are estimated as the sum of the emissions from screening and fugitive sources.

1,597 + 8,134 = 9,731pounds = 4.9 tons PM10

Table 4 tabulates PM10 emissions from construction sand processing for each county of California. (These emissions should be reduced by reasonable control efficiencies if wet handling is known to occur.)

9

Table 3. Annual PM10 emissions from construction gravel manufacturing.

County Name

No. of Employees (or range midpoint)

% of State Production

Total Gravel Production

(tons)

Screening Emissions

(tons)

Crushing Emissions

(tons)

Fugitive Emissions

(tons)

Total Emissions

(tons)Alameda 333 10.72% 8,863,700 150.2 2.8 405.1 558.1Amador 2 0.06% 53,200 0.90 0.02 2.4 3.4Butte 2 0.06% 53,200 0.90 0.02 2.4 3.4Calaveras 2 0.06% 53,200 0.90 0.02 2.4 3.4Contra Costa 14.5 0.47% 386,000 6.5 0.12 17.6 24.3El Dorado 64.5 2.08% 1,716,800 29.1 0.54 78.5 108.1Fresno 174.5 5.62% 4,644,800 78.7 1.4 212.3 292.4Imperial 2 0.06% 53,200 0.90 0.02 2.4 3.4Kern 72 2.32% 1,916,500 32.5 0.60 87.6 120.7Los Angeles 395 12.72% 10,513,900 178.2 3.3 480.5 662.0Madera 35 1.13% 931,600 15.8 0.29 42.6 58.7Mendocino 30 0.97% 798,500 13.5 0.25 36.5 50.3Merced 6 0.19% 159,700 2.7 0.05 7.3 10.1Monterey 17 0.55% 453,000 7.7 0.14 20.7 28.5Nevada 32.5 1.05% 865,100 14.7 0.27 39.5 54.5Orange 174.5 5.62% 4,644,800 78.7 1.4 212.3 292.4Placer 74.5 2.40% 1,983,000 33.6 0.62 90.6 124.9Plumas 4 0.13% 106,500 1.8 0.03 4.9 6.7Riverside 374.5 12.06% 9,968,300 169.0 3.1 455.6 627.6Sacramento 175 5.63% 4,658,100 79.0 1.5 212.9 293.3San Benito 7.5 0.24% 199,600 3.4 0.06 9.1 12.6San Bernardino

181 5.83% 4,817,800 81.7 1.5 220.2 303.3

San Diego 220 7.08% 5,855,900 99.3 1.8 267.6 368.7San Joaquin 110 3.54% 2,927,900 49.6 0.91 133.8 184.3San Luis Obispo

5 0.16% 133,100 2.3 0.04 6.1 8.4

Santa Barbara 30 0.97% 798,500 13.5 0.25 36.5 50.3Santa Cruz 32.5 1.05% 865,100 14.7 0.27 39.5 54.5Shasta 7.5 0.24% 199,600 3.4 0.06 9.1 12.6Solano 59.5 1.92% 1,583,700 26.8 0.49 72.4 99.7Sonoma 102 3.28% 2,715,000 46.0 0.85 124.1 170.9Stanislaus 34 1.09% 905,000 15.3 0.28 41.4 57.0Sutter 2 0.06% 53,200 0.90 0.02 2.4 3.4Tehama 9.5 0.31% 252,900 4.3 0.08 11.6 15.9Trinity 14.5 0.47% 386,000 6.5 0.12 17.6 24.3Tulare 53 1.71% 1,410,700 23.9 0.44 64.5 88.8Ventura 174.5 5.62% 4,644,800 78.7 1.4 212.3 292.4Yolo 70 2.25% 1,863,200 31.6 0.58 85.1 117.3Yuba 9.5 0.31% 252,900 4.3 0.08 11.6 15.9Totals 3,106.50 82,687,500 1,401.6 25.8 3,778.8 5,206.2

10

Table 4. Annual PM10 emissions from construction sand manufacturing.

County NameTotal Sand

Production (tons)Screening Emissions

(tons)Fugitive Emissions

(tons)Total Emissions

(tons)Alameda 8,863,700 133.0 677.2 810.1Amador 53,200 0.80 4.1 4.9Butte 53,200 0.80 4.1 4.9Calaveras 53,200 0.80 4.1 4.9Contra Costa 386,000 5.8 29.5 35.3El Dorado 1,716,800 25.8 131.2 156.9Fresno 4,644,800 69.7 354.9 424.5Imperial 53,200 0.80 4.1 4.9Kern 1,916,500 28.7 146.4 175.2Los Angeles 10,513,900 157.7 803.3 961.0Madera 931,600 14.0 71.2 85.1Mendocino 798,500 12.0 61.0 73.0Merced 159,700 2.4 12.2 14.6Monterey 453,000 6.8 34.6 41.4Nevada 865,100 13.0 66.1 79.1Orange 4,644,800 69.7 354.9 424.5Placer 1,983,000 29.7 151.5 181.2Plumas 106,500 1.6 8.1 9.7Riverside 9,968,300 149.5 761.6 911.1Sacramento 4,658,100 69.9 355.9 425.7San Benito 199,600 3.0 15.3 18.2San Bernardino 4,817,800 72.3 368.1 440.3San Diego 5,855,900 87.8 447.4 535.2San Joaquin 2,927,900 43.9 223.7 267.6San Luis Obispo 133,100 2.0 10.2 12.2Santa Barbara 798,500 12.0 61.0 73.0Santa Cruz 865,100 13.0 66.1 79.1Shasta 199,600 3.0 15.3 18.2Solano 1,583,700 23.8 121.0 144.8Sonoma 2,715,000 40.7 207.4 248.2Stanislaus 905,000 13.6 69.1 82.7Sutter 53,200 0.8 4.1 4.9Tehama 252,900 3.8 19.3 23.1Trinity 386,000 5.8 29.5 35.3Tulare 1,410,700 21.2 107.8 128.9Ventura 4,644,800 69.7 354.9 424.5Yolo 1,863,200 27.9 142.4 170.3Yuba 252,900 3.8 19.3 23.1Totals 82,687,500 1,240.3 6,317.3 7,557.6

11

Industrial Sand Processing Emissions

County-level production of industrial sand is estimated by apportioning statewide production according to county-level employment data for the Industrial Sand Mining Sector (NAICS code 212322). The Census Bureau reports that there is one industrial sand mining facility in Amador County with 20 to 50 employees, the midpoint of which is equal to 35 employees (US Census Bureau, 2001). The number of employees per county is divided by the total number of employees for the state to derive the proportion of state production.

35 employees (Amador) ÷ 111 employees (California) = 0.3153

This proportion is multiplied by the state production to estimate the production of industrial-grade sand in Amador County.

0.3153 2,006,550 tons = 632,696 tons of industrial sand

The PM10 emissions due to crushing processes are calculated by multiplying production by the corresponding emission factors (see Table 1). Based on information acquired from industry contacts, only 75% of produced industrial sand is typically routed through primary crushing and 15% is routed through secondary crushing (see Figure 2). After initial crushing, all of the material is ground by a mill to reduce the material to a size of 50 micrometers or less. AP-42 did not provide emission factors for the grinding process, so the emissions generated by grinding were assumed to be similar to those for fines crushing.

632,696 tons [0.0024 lb/ton (75% + 15%) + 0.015] = 10,857 pounds PM10 = 5.4 tons PM10

Before and between crushing, the fine silica or quartz materials are screened multiple times to achieve the required grain size. The early screening processes employ aggregate screens rather than fines screens. Lastly, all of the sand is sized, which is normally a process that involves a control technology such as a Venturi scrubber (see Table 2). The PM10 emissions for these processes are estimated as follows.

632,696 tons [0.015 (2 + 75% + 15%) + 0.0021)] = 28,851 pounds PM10 = 14 tons PM10

Fugitive emission sources for a typical plant include wet drilling, truck unloading of fragmented stone, six processes that involve sand handling, grinding and transfer points, three continuous conveyor drops onto piles, and materials storage. Emission factors for these activities, which are listed in Table 2, are proportioned according to the counts of similar emissions points at a typical facility (e.g., 6 transfer points, 3 conveyer drops, etc.).

632,696 tons [0.00008 + 0.000016 + (6 0.0013) + (3 0.06) + 0.0013] = 119,703 pounds = 60 tons PM10

Drying is the final processing step for industrial sand. This process generates combustion by-products and geologic dust emissions. Available AP-42 PM10 emission factors are for uncontrolled sand drying and sand drying with common control devices such as wet scrubbers or

12

fabric filters. Uncontrolled sand dryers are uncommon because the PM10 emissions are high. Therefore, we have assumed use of wet scrubber control technology for these calculations.

632,696 tons 0.039 lb/ton = 24,675 pounds PM10 = 12 tons PM10

Total PM10 emissions for the processing of industrial sand are estimated as the sum of the emissions from crushing, screening, fugitive, and sand drying activities.

10,875 + 28,851 + 119,703 + 24,675 = 184,104 pounds = 92 tons PM10

The results of these PM10 calculations for every county in California that has employment in the Industrial Sand Mining sector are shown in Table 5. (These emissions should be reduced by reasonable control efficiencies if wet handling is known to occur.)

Table 5. Annual PM10 emissions from industrial sand manufacturing.

County Name

No. of Employees (or range midpoint)

% of State Production

Total Sand Production

(tons)

Screening Emissions

(tons)

Crushing Emissions

(tons)

Fugitive Emissions

(tons)

Drying Emissions

(tons)

Total Emissions

(tons)Amador 35 31.53% 632,696 14.4 5.4 59.9 12.3 92.0Contra Costa 35 31.53% 632,696 14.4 5.4 59.9 12.3 92.0Kern 2 1.80% 36,154 0.82 0.31 3.4 0.71 5.3Los Angeles 2 1.80% 36,154 0.82 0.31 3.4 0.71 5.3Orange 35 31.53% 632,696 14.4 5.4 59.9 12.3 92.0Riverside 2 1.80% 36,154 0.82 0.31 3.4 0.71 5.3Totals 111 100 2,006,550 45.7 17.2 189.8 39.1 291.9

In addition to geologic PM10 emissions, emissions of fuel combustion by-products from the sand drying process were estimated. These emissions are attributed to the “Industrial Natural Gas Combustion (Unspecified)” category of the emission inventory. EPA’s guidance document, AP-42, presents NOx and CO2 emission factors for natural gas-powered sand dryers. Corresponding emission factors for CO, SO2, and VOCs were unavailable. Therefore, emissions factors were adapted for use from Chapter 1.4 of AP-42, which covers natural gas combustion. The emission factors for sand and gravel dryers (in units of mass per ton of sand dried) were not directly comparable to the emission factors for natural gas external combustion (in units of mass per million standard cubic feet of natural gas consumed). Therefore, near complete conversion of methane to CO2 was assumed in order indirectly estimate the quantity of natural gas consumed per ton of sand dried and to estimate CO, SO2, and VOC emission factors.

From Chapter 1.4, the ratio of SO2 emissions to CO2 emissions was estimated. (This assumes that the H2S content of the natural gas is 3.18 ppmv.)

0.6 lb SO2/106 scf 120,000 lb CO2/106scf = 0.000005 units SO2 per unit CO2

13

This proportion is then applied to the CO2 emission factor for sand dryers to estimate the SO2 emission factor.

0.000005 27 lb CO2/ton sand = 0.000135 lb SO2/ton sand

Similarly, VOC and CO emission factors are estimated to be 0.00124 lb VOC/ton sand and 0.0189 lb CO/ton sand. These emission factors are multiplied by the total industrial sand production for Amador County to estimate emissions of combustion by-products for the sand dryer.

632,696 tons 0.000135 lb SO2/ton = 85 pounds SO2 = 0.04 tons SO2

632,696 tons 0.00124 lb VOC/ton = 785 pounds VOC = 0.39 tons VOC

632,696 tons 0.0189 lb CO/ton = 11,958 pounds CO = 6.0 tons CO

632,696 tons 0.031 lb NOx/ton = 19,614 pounds NOx = 9.8 tons NOx

Table 6 tabulates combustion by-product emissions from sand dryers for each county in California that has employment in the Industrial Sand Mining sector.

Table 6. Annual emissions of combustion by-products from industrial sand drying.a

County NameTotal Sand

Production (tons) NOx (tons) CO (tons) SOx (tons) VOC (tons)Amador 632,696 9.8 6.0 0.043 0.39

Contra Costa 632,696 9.8 6.0 0.043 0.39Kern 36,154 0.56 0.34 0.00 0.02

Los Angeles 36,154 0.56 0.34 0.00 0.02Orange 632,696 9.8 6.0 0.043 0.39

Riverside 36,154 0.56 0.34 0.00 0.02Totals 2,006,550 31.1 19.0 0.14 1.24

a Emissions from the sand dryer, which are natural gas combustion by-products, are included in the “Industrial Natural Gas Combustion (Unspecified)” source category.

14

GRINDING AND CRUSHING OF AGGREGATES

Grinding and crushing of aggregates involves many of the same activities as sand/gravel processing (sizing, screening, transferring) and in addition, involves crushing the raw materials (mined or quarried rock) multiple times into smaller aggregates or manufactured sand. Many of the end uses of crushed stone are similar to construction sand and gravel, such as the construction of roads and production of asphalt or concrete. However, there are some key differences between as well. Unlike sand or gravel, the raw material for crushed rock tends to be large quantities of uniform rock deposits, which makes it more aesthetically suitable for certain applications, such as landscaping. Some additional unique applications for crushed rocks are foundation for roads, pipe bedding, and rip rap. These uses require more coarsely graded materials than can be obtained from sand and gravel producers. The EPA’s document, AP-42, provides emissions estimation guidance for sand and gravel production processes.

Grinding and Crushing Process Overview and Associated Emissions

Aggregate crushing is more emissions intensive than sand or gravel processing. Emission factors are applied proportionally according to the number of process repetitions that occur at a typical plant, and according to the relative quantities of material that re-route through iterations of crushing-and-screening stages. For this guidance, we have formulated a process diagram for a typical crushed stone plant on the basis of reference materials, staff members’ advice from the National Stone, Sand and Gravel Association, and a tour of a crushed stone facility (see Figure 3) (Hayden, pers. comm., 2001; National Stone Association, 1995; EPA, 1996). There are emissions associated with increased activity such as wet drilling and blasting of raw material, transportation of material, repeated crushing and sizing, and additional load drops and transfer points. Drilling or blasting techniques, or a combination of these, are used to loosen the raw material. Typically, five occurrences of truck unloading occur throughout the production process. At the first unloading, the material is fragmented stone from the quarry, while the other three are batch drops. One truck unloads its material to begin the conveyor process. Normally, five conveyor transfer points and one continuous drop are part of the production process. In the crushed aggregates industry, raw materials are sized and crushed iteratively up to four times to obtain the correct size aggregate. Each time the load is crushed, the material must be re-sized and sorted, such that larger aggregates are routed for additional crushing. Figure 3 indicates the fractional proportions of the initial material that typically must be ground and re-screened at each of these stages, but these proportions vary by facility. After screening, different size categories are routed differently throughout the plant.

15

Figure 3. Process diagram for a typical crushed stone facility.

16

Some plants operate a crusher and screen that process sand, or “fines”, which are produced from friable raw material (e.g., sandstone). The finished product is called manufactured sand. The screening process separates the fines from the rest of the raw material. Portions of the sand are re-screened and re-crushed as needed by machinery that is designed to produce manufactured sand. Unless wet suppression techniques are used, processing of fines results in high emissions. However, manufactured sand accounts for a very small fraction of the crushed stone industry because less expensive alternatives, namely construction sand, are available. The production of manufactured sand also varies geographically due to the availability of construction sand. Regions that have limited access to river sand deposits may consume a much higher proportion of manufactured sand than other regions.

EPA (1996) provides emission factors for processes at crushed stone plants (see Table 7). Table 7 lists the emission rates for PM and PM10 from sources that are uncontrolled (unless otherwise specified). Emission factors for primary and secondary crushing are not available, so the emission rate for tertiary crushing is applied to all crushing processes for a conservatively high emissions estimate.

Table 7. PM10 emission factors for crushed stone facilities (EPA, 1996; EPA, 1995a; National Stone Association, 1995).

Process PMa (lb/ton) PM10 (lb/ton)Conveyor transfer point NA 0.0014Truck loading by conveyor NA 0.00010Truck unloading of fragmented stone

NA 0.000016

Truck batch drop 0.24 0.0024Wet drilling (moisture controlled) NA 0.00008

17

Screening of crushed material NA 0.015Primary, secondary, and tertiary crushing

0.036 0.0024

Uncontrolled storage piles 0.043 0.020Fines crushing 0.72 0.015Fines screening NA 0.071

a NA means “not available”. When emission factors for total PM10 are not available those for PM are used.

In addition, AP-42 presents the following equation to estimate emissions from blasting at surface coal mines (EPA, 1995a). This equation was adapted for application to rock quarries.

EF = 0.52 1.4(10-5) A1.5

where EF = Emission factor, pounds PM10 per blastA = Horizontal surface area of blast (square feet)

To estimate the surface area of the blast, several factors are needed. Anecdotal evidence from various sources was reviewed (including news articles, promotional brochures for the explosives industry, and state permitting documents) to estimate the typical quantity of explosives used per blast and the typical mass of material excavated from each blast. From this information, the volume of the raw material and the radius of impact for a typical blast were estimated. The radius of impact (r) was used to estimate the surface area of blast (A).

At rock mines, the amount of explosives per blast at rock mines seems to range between 1 to 2.2 tons. Each blast tends to loosen 5,000 to 15,000 tons of rock. From the anecdotal evidence, one blast impacts approximately 9000 tons of material or 4030 cubic yards of rock (rock density of approximately 2.2 tons per cubic yard is assumed). If a blast erupts an inverted dome-shaped quantity of rock, then the volume equals (4/6) r3 = 4030 cubic yards. Thus, r =12.4 cubic yards or about 37 feet. This is taken as the horizontal impact radius. The surface area of blast (A) equals r2 = 4374 square feet. Therefore, the emission factor for blasting is estimated as follows.

EF = 0.52 1.4(10-5) 43741.5 = 2.1 lb PM10 per blast

Activity Data

The USGS, in cooperation with the California Department of Conservation, estimated 1999 statewide production of crushed stone to be 55,000,000 metric tons, or 60,637,500 tons (USGS, 2001a). Industry professionals estimate that manufactured sand comprises 10% of total crushed stone production (Hayden, pers. comm., 2001). While economic growth from 1999 to 2000 was significant for some sections of California’s nonmetallic minerals and construction industries (from 0.1 to 7% growth) (California Employment Development Department, 2001), this should introduce a small error in the emissions estimates (much less than 10%). Therefore, 1999 and 2000 statewide production levels are assumed to be equal. The US Census Bureau “County Business Patterns” database provides county-level employment data for the Stone

18

Mining and Quarrying Sector, which is designated by NAICS code 21231X (US Census Bureau, 2001). These employment data were used to disaggregate statewide production of crushed stone to estimate county-level productions.

Temporal Allocation

The same seasonal pattern that was developed for sand and gravel processing emissions, shown below, is applied for crushed stone processing emissions.

January through March, 18.8% April through June, 25.6% July through September, 28.1% October through December, 27.6%

In addition, the same weekly and diurnal pattern is used: 12 hours per day and six days per week (Sundays off).

Additional Considerations

Issues that were discussed in the previous section for construction sand and gravel are also valid for the crushed stone industry. Emission factors are, in many cases, worst-case and variable with site-specific silt contents and local weather conditions.

Example Calculation for Aggregate Crushing

To excavate 60,637,000 tons of crushed stone in California, around 6,700 blasts are required (approximately 61 million tons material ÷ 9000 tons material per blast). Emissions of PM10 due to blasting at rock mines are calculated as follows.

2.1 lbPM/blast 6,700 blasts = 14,100 pounds = 7.1 tons PM10

As an independent check of this calculations, it was noted that the USGS (2001a) reports that 34,700 tons of explosives were sold in California in 1997, 37,200 in 1998 and 34,400 in 1999. Quarrying accounted for 13-14% of explosive sales in the US (USGS, 2001a). However, other major uses of explosives across the US are coal mining (67%), metal mining (10%), and construction work (7%) (USGS, 2001a). Coal mining is negligible in California; therefore, the above national percentages are not likely to be accurate for the state. The federal percentages were normalized according to numbers of mines in 1999 (see Table 8) to estimate the percentage of explosives used for quarrying in California (18.9%), (or 5.4 28.5 100%). If 6,560 tons of explosives (or 18.9% of 34,700 tons) were used at California rock quarries at a rate of 1 to 2.2 tons of explosives per blast, this equates to approximately 3,000 to 6,600 blasts. This range is reasonably close to the estimate of 6,700 blasts presented above.

19

Table 8. Mining and construction activity parameters for California and the US (USGS, 2001a).

IndustryCalifornia Activity

US Activity

California % of

US Activity

Normalized California

% ofActivity

Coal mining – No. of mines 3 1336 0.2 0.7Quarrying – No. of mines 295 5,415 5.4 18.9Metal Mining – No. of mines 61 529 11.5 40.3Construction – No. of employees 706,000 6,202,000 11.4 40.0

Totals 28.5% 100%

Production of crushed stone for Amador County was calculated by using employment data for the Stone Mining and Quarrying Sector (NAICS code 21231X). The Census Bureau reports 2 stone crushing facilities in Amador County with total employment from 10 to 20 employees, the midpoint of which equals 15 employees. The number of employees per county is divided by the total number of employees for the state to derive the proportion of state production.

15 employees (Amador) ÷ 2,032 employees (California) = 0.0074

This proportion is multiplied by the state production to estimate the production of crushed stone in Amador County.

0.0074 60,637,500 tons = 447,500 tons of crushed stone

In addition, this proportion is used to estimate Amador’s PM10 emissions from blasting operations at crushed stone facilities.

0.0074 14,100 pounds PM10 = 104 pounds PM10 = 0.05 tons PM10

The PM10 emissions due to primary, secondary, and tertiary crushing processes are calculated by multiplying the county production of crushed stone by the corresponding emission factors and processing fractions (see Table 7 and Figure 3).

447,500 tons 0.0024 lb/ton (75% + 50% + 25%) = 1,611 pounds PM10

= 0.81 tons PM10

The first screen in the production process separates the fines from the oversized materials and directs the majority of the material to the second screen for sizing. The fines are removed from further processing and the oversized materials are directed to the secondary crusher. The material from both the secondary crusher and the “throughs” from first screen, which together

20

comprise about 95% of the total material, are sized by the secondary screen. The secondary screen roughly sizes all of the material, except the extremely fine materials, and directs the oversized material to be crushed for a third time. The PM10 emissions from primary, secondary, and tertiary screening processes are estimated as follows.

447,500 tons 0.015 lb/ton (100% + 95% +25%) = 14,768 pounds PM10 = 7.4 tons PM10

Fugitive emission sources include wet drilling of raw materials, truck unloading of fragmented stone, truck loading by conveyor, one continuous drop by conveyor to form a pile, five conveyor transfer points, three truck batch drops, and storage of materials. Emissions for these sources are estimated below.

447,500 tons [0.00008 + 0.000016 + 0.0001 + 0.06 + (5 0.0014) + (3 0.0024) + 0.02] lb/ton

= 42,243 pounds PM10 = 21 tons PM10

Total PM10 emissions for the processing of crushed stone equal the sum of the emissions from blasting, crushing, screening, and fugitive sources.

104 + 1611 + 14,768 + 42,243 = 58,726 pounds = 29 tons PM10

Manufactured sand undergoes additional processing steps, including fines crushing and screening. Industry professionals estimate that only 10% of crushed stone production is manufactured sand (Hayden, 2001). Thus, plants in Amador County produced 44,750 tons of manufactured sand (or 10% of 447,500 tons). It is estimated that only half of all fines need to be crushed once or twice to reduce their diameter to the required size. PM10 emissions due to fines crushing are estimated as shown below.

44,750 tons (0.015 lb/ton 50%) = 336 pounds PM10 = 0.17 tons PM10

All of the sand is screened once and the fraction that is crushed is screened again. The PM10 emissions from fines screening are estimated below.

44,750 tons [0.071+(50% 0.071)] = 4767 pounds PM10 = 2.4 tons PM10

Fugitive emissions from manufactured sand production include two conveyor transfer points, a continuous conveyor drop, materials storage, and an additional batch drop.

44,750 tons [(2 0.0014) + 0.06 + 0.02 + 0.0024] lb/ton = 3813 pounds PM10 = 1.9 tons PM10

The total PM10 emissions for the additional manufactured sand processing steps are estimated as the sum of the emissions from blasting, crushing, screening, and fugitive sources.

336 + 4767 + 3813 = 8916 pounds = 4.5 tons

21

Thus, the total PM10 emissions from the crushed stone and manufactured sand industry are the emissions from stone crushing plus those from manufactured stone production. For Amador County this is 67,600 pounds, or about 34 tons of PM10. The PM10 emissions from crushed stone processing and manufactured sand processing are located in Tables 9 and 10.

22

Table 9. Annual PM10 emissions from crushed stone processing.

County Name

No. of Employees (or range midpoint)

% of State Production

Total Stone Production

(tons)

Blasting Emissions

(tons)Screening

Emissions (tons)Crushing

Emissions (tons)

Fugitive Emissions

(tons)Total Emissions

(tons)Alameda 69.5 3.42% 2,073,500 0.241 34.2 3.7 97.9 136.0Amador 15 0.74% 447,500 0.052 7.4 0.81 21.1 29.4Butte 14.5 0.71% 432,600 0.050 7.1 0.78 20.4 28.4Contra Costa 69.5 3.42% 2,073,500 0.241 34.2 3.7 97.9 136.0El Dorado 14.5 0.71% 432,600 0.050 7.1 0.78 20.4 28.4Fresno 59.5 2.93% 1,775,100 0.206 29.3 3.2 83.8 116.5Imperial 59.5 2.93% 1,775,100 0.206 29.3 3.2 83.8 116.5Kern 64.5 3.17% 1,924,300 0.224 31.8 3.5 90.8 126.3Lake 2 0.10% 59,700 0.007 1.0 0.11 2.8 3.9Los Angeles 162 7.97% 4,833,100 0.562 79.7 8.7 228.1 317.1Madera 7 0.34% 208,800 0.024 3.4 0.4 9.9 13.7Mariposa 2 0.10% 59,700 0.007 1.0 0.11 2.8 3.9Mendocino 2 0.10% 59,700 0.007 1.0 0.11 2.8 3.9Merced 14.5 0.71% 432,600 0.050 7.1 0.78 20.4 28.4Modoc 14.5 0.71% 432,600 0.050 7.1 0.78 20.4 28.4Monterey 2 0.10% 59,700 0.007 1.0 0.11 2.8 3.9Nevada 44.5 2.19% 1,327,600 0.154 21.9 2.4 62.7 87.1Orange 50 2.46% 1,491,700 0.173 24.6 2.7 70.4 97.9Placer 14.5 0.71% 432,600 0.050 7.1 0.78 20.4 28.4Plumas 2 0.10% 59,700 0.007 1.0 0.11 2.8 3.9Riverside 187 9.20% 5,579,000 0.649 92.1 10.0 263.3 366.1San Benito 42 2.07% 1,253,000 0.146 20.7 2.3 59.1 82.2San Bernardino 214.5 10.55% 6,399,400 0.744 105.6 11.5 302.0 419.9San Diego 209.5 10.31% 6,250,200 0.727 103.1 11.3 295.0 410.1San Joaquin 7 0.34% 208,800 0.024 3.4 0.38 9.9 13.7San Luis Obispo 174.5 8.59% 5,206,000 0.605 85.9 9.4 245.7 341.6San Mateo 74.5 3.67% 2,222,600 0.258 36.7 4.0 104.9 145.8

23

Table 9. Annual PM10 emissions from crushed stone processing.

County Name

No. of Employees (or range midpoint)

% of State Production

Total Stone Production

(tons)

Blasting Emissions

(tons)Screening

Emissions (tons)Crushing

Emissions (tons)

Fugitive Emissions

(tons)Total Emissions

(tons)Santa Barbara 7 0.34% 208,800 0.024 3.4 0.38 9.9 13.7Santa Clara 74.5 3.67% 2,222,600 0.258 36.7 4.0 104.9 145.8Santa Cruz 174.5 8.59% 5,206,000 0.605 85.9 9.4 245.7 341.6Shasta 14.5 0.71% 432,600 0.050 7.1 0.78 20.4 28.4Siskiyou 2 0.10% 59,700 0.007 1.0 0.11 2.8 3.9Sonoma 64.5 3.17% 1,924,300 0.224 31.8 3.5 90.8 126.3Stanislaus 14.5 0.71% 432,600 0.050 7.1 0.78 20.4 28.4Sutter 7 0.34% 208,800 0.024 3.4 0.38 9.9 13.7Tuolumne 79.5 3.91% 2,371,800 0.276 39.1 4.3 111.9 155.6Ventura 2 0.10% 59,700 0.007 1.0 0.11 2.8 3.9Totals 2032.5 1.0 60,637,500 14,100.000 1,001 109 2,862 3,978.7

24

Table 10. Annual PM10 emissions from manufactured sand production.

County Name

Total Sand Production

(tons)Fines Crushing

Emissions (tons)Fines Screening Emissions (tons)

Fugitive Emissions

(tons)

Total Emissions

(tons)Alameda 207,350 0.78 11.0 8.8 20.7Amador 44,750 0.17 2.4 1.9 4.5Butte 43,260 0.16 2.3 1.8 4.3Contra Costa 207,350 0.78 11.0 8.8 20.7El Dorado 43,260 0.16 2.3 1.8 4.3Fresno 177,510 0.67 9.5 7.6 17.7Imperial 177,510 0.67 9.5 7.6 17.7Kern 192,430 0.72 10.2 8.2 19.2Lake 5,970 0.02 0.3 0.3 0.6Los Angeles 483,310 1.81 25.7 20.6 48.1Madera 20,880 0.08 1.1 0.9 2.1Mariposa 5,970 0.02 0.3 0.3 0.6Mendocino 5,970 0.02 0.3 0.3 0.6Merced 43,260 0.16 2.3 1.8 4.3Modoc 43,260 0.16 2.3 1.8 4.3Monterey 5,970 0.02 0.3 0.3 0.6Nevada 132,760 0.50 7.1 5.7 13.2Orange 149,170 0.56 7.9 6.4 14.9Placer 43,260 0.16 2.3 1.8 4.3Plumas 5,970 0.02 0.3 0.3 0.6Riverside 557,900 2.09 29.7 23.8 55.6San Benito 125,300 0.47 6.7 5.3 12.5San Bernardino 639,940 2.40 34.1 27.3 63.7San Diego 625,020 2.34 33.3 26.6 62.3San Joaquin 20,880 0.08 1.1 0.9 2.1San Luis Obispo 520,600 1.95 27.7 22.2 51.9San Mateo 222,260 0.83 11.8 9.5 22.1Santa Barbara 20,880 0.08 1.1 0.9 2.1Santa Clara 222,263 0.83 11.8 9.5 22.1Santa Cruz 222,260 1.95 27.7 22.2 51.9Shasta 43,260 0.16 2.3 1.8 4.3Siskiyou 5,970 0.02 0.3 0.3 0.6Sonoma 192,430 0.72 10.2 8.2 19.2Stanislaus 43,260 0.16 2.3 1.8 4.3Sutter 20,880 0.08 1.1 0.9 2.1Tuolumne 237,180 0.89 12.6 10.1 23.6Ventura 5,970 0.02 0.3 0.3 0.6Totals 6,063,750 22.7 322.9 258.3 603.9

25

CEMENT CONCRETE PRODUCTION

Two industry categories comprise cement concrete production: cement manufacturing, and concrete production. Cement is a very fine powder used as the chief binding element in concrete products. Calcareous raw materials, such as limestone, chalk, marl, seashells, or aragonite are used to manufacture cement. Concrete is a combination of cement powder, water, sand, and course aggregates. These ingredients are blended together and used at construction sites. Emissions from cement production are a subset of the total emissions from concrete manufacturing.

Portland Cement Process Overview and Associated Emissions

There are only a few Portland cement facilities in the State of California and they are potentially large emissions sources – large enough to be included in the point source inventory. A discussion of top-down emissions calculations is provided in this section; however, it is recommended that this source is included with the point source inventory rather than the area source inventory.

Portland cement accounts for 95% total US cement production and 96.1% of California cement production (USGS, 2001a). The remaining 3.9% of California’s cement is produced as masonry cement (USGS, 2001a). Both portland cement and masonry cement are categorized as hydraulic cements. (Other hydraulic cements are pozzalanic and naturally occurring cement rock.) The primary difference between masonry cement and portland cement is that masonry cement, which is used for brick or stone work, requires different levels of calcium and tolerances for impurities. However, the two types of cement are manufactured via similar processes. Therefore, emissions estimation techniques are similar.

Cement is comprised of four mineral types: calcareous, aluminous, ferrous, and siliceous. Limestone is the predominant calcium source for cement manufacturing because it is naturally calcium rich in calcium carbonate (CaCO3). Limestone accounts for 64% by weight of the raw materials used in portland cement production (USGS, 2001a). For economic reasons, the cement industry is shifting to the use of waste materials, such as fly ash, mill scale, and various types of slag, to produce blended cements.

The production of portland cement involves several steps: raw material excavation or purchasing, grinding and blending of raw materials, kiln production of cement clinker, and fine grinding and blending to achieve a final product. Portland cement is manufactured by mixing, heating, and liquefying raw materials in a rotary kiln to produce “clinker,” or dense nodules of cementatious material. Approximately one-third of the mass of the raw stone is lost as carbon dioxide (CO2), a by-product of the calcination of limestone (EPA, 1995b). The temperature in the kiln needs to be high enough to promote chemical reactions between the raw materials and to calcinate the limestone, evaporate volatile impurities, and amalgamate calcium oxides with oxides of silica, aluminum, and iron. For these reactions to occur, the temperature inside the kiln must reach 1510 degrees Celsius (2750 degrees Fahrenheit). This requires a fuel source, such as

26

natural gas (which is typical), coal, oil, petroleum coke, or waste fuels such as waste solvents or rubber from used tires. The kiln exhaust contains by-products of combustion and products of the chemical breakdown of the raw material. The emission factors reported by the EPA do not differentiate between the emissions sources for the kiln process emissions (EPA, 1995b). Therefore, all the emissions from cement kilns are included in the cement concrete EIC category.

Four processes may be used to manufacture portland cement (in decreasing order of energy requirements): the wet process, the long dry process, the dry process with a preheater, or the dry process with a preheater/precalciner. The wet process requires that water is added during the raw materials preparation phase, which suppresses PM and PM10 emissions during handling of raw materials until kiln processing is complete. Both the preheater and preheater/precalciner are optional preparatory steps. These steps use hot exit gases from the kiln to jump-start chemical reactions before the raw material enters the rotary kiln. Although this relatively efficient use of energy reduces emissions associated with fuel use, carbon monoxide emissions increase considerably due to the altered chemical reactions.

After kiln processing, clinker is converted to portland cement by adding gypsum or anhydrite (forms of calcium sulfate) and milling the nodules into a fine powder. Calcium sulfate controls the setting time of the cement. In order for the concrete product to be durable and strong, the cement should not harden too quickly (Portland Cement Association, 2001). Portland cement powder is stored in large silos for bulk shipments and some is packaged for retail.

EPA (1995b) provides emission factors for portland cement kiln processing (see Table 11). Although other sources of SO2, NOx, CO, and TOC emissions exist at a portland cement manufacturing plant, the kiln process produces the majority of these emissions.

Table 11. Combustion product emission factors for cement kilns(EPA, 1995b).

Kiln typeSO2 (lb/ton clinker

produced)aNOx (lb/ton clinker

produced)CO (lb/ton clinker

produced)TOC (lb/ton clinker

produced)Wet Process 8.2 7.4 0.12 0.028Dry Process 10 6.0 0.21 0.028Preheater 0.55 4.8 0.98 0.18Preheater/Precalciner

1.1 4.2 3.7 0.12

a Uncontrolled emission factors used for SO2, assume a 99.9% reduction in SO2 due to absorption into the cement product (Minin, 2002). Confidence in the emission factor for SO2 from cement kilns is low. EPA (1995b) suggests that a mass balance of sulfur, which requires site-specific data, is a superior estimation method.

Because PM emissions from kiln processes are so large, vent stacks are equipped with air pollution controls, such as electrostatic precipitators (ESP) or fabric filters. Other sources of PM and PM10 emissions are raw material storage, drying, blending and sizing, kiln feed preparation, finish grinding and blending, packaging, and fugitive sources. EPA (1995b) recommends the emission factors listed in Table 12 to estimate PM and PM10 emissions from portland cement production.

27

Table 12. PM and PM10 emission factors from cement production (EPA, 1995b).

ProcessPM

(lb/ton material)PM10

(lb/ton material)a

Wet process kiln (uncontrolled)b 130 31Wet process kiln with ESP b 0.77 0.65Dry process kiln with ESP b,e 1.0 0.84Preheater kiln (uncontrolled)b 250 NAPreheater kiln with ESP b,e 0.26 0.218Preheater/Precalciner kiln with ESP b,e 0.21 0.176Clinker cooler with grave bed filter b 0.21 0.16Raw mill with fabric filter c 0.012 NARaw mill feed belt with fabric filter c 0.0031 NARaw mill weigh hopper with fabric filter c 0.019 NARaw mill air separator with fabric filter c 0.032 NAFinish grinding mill with fabric filter d 0.0080 NAFinish grinding mill feed belt with fabric filter d 0.0024 NAFinish grinding mill weigh hopper with fabric filter d 0.0094 NAFinish grinding mill air separator with fabric filter d 0.028 NAa NA indicates “not available”. When emission factors for total PM10 are not available those for PM are used.

b Units from kiln processes are expressed in terms of pounds per ton of clinker product. c Units from raw material handling are expressed in terms of pounds per ton of raw material. d Units from final processing are expressed in terms of pounds per ton total material. e For kiln PM10 emissions, the EPA reported cumulative mass percent of PM (0.84 for controlled dry process kilns) was multiplied by the PM emission factor to obtain the resulting PM10 emission factor.

Activity Data

The USGS, in conjunction with the California Department of Conservation, published total 1999 statewide production of portland cement and masonry cement (USGS, 2001a).

Portland cement production was 10,300,000 metric tons in California, which is equal to 11,355,800 tons.

Masonry cement production in California was 420,000 metric tons, which is equivalent to 463,000 tons.

Total California cement production was 11,818,800 tons.

The portland and masonry cement industry experienced more than five percent growth nationwide from 1999 to 2000 (California Employment Development Department, 2001). Therefore, 1999 California production data was increased by 5% to estimate year 2000 cement production in the state of California.

28

Portland cement production for year 2000 in California is estimated to be 11,923,500 tons Masonry cement production in California for year 2000 is estimated to be 486,200 tons Total California cement production for year 2000 is 12,409,700 tons

The US Census Bureau “County Business Patterns” database includes employment data for the cement industry for California and its counties (US Census Bureau, 2001). Data were acquired for the Cement Manufacturing Sector (NAICS 327310), which were used to disaggregate statewide production of cement to estimate county-level productions.

Temporal Allocation

Emissions are assumed to be continuous year round. Diurnal variation varies by process type. The emissions from kiln activity (includes PM emissions and fuel combustion by-products) are assumed to be continuous (24 hours a day, seven days a week). It is recommended that for the remaining processes for portland cement production (raw milling, finish grinding and handling, and finishing processes), the diurnal variation of a typical construction work week is assigned (12 hours a day, six days a week).

Additional Considerations

The emission factors for SO2 as reported by the EPA are very high. The EPA cites that the emissions for SO2 would be more accurate if a mass balance on sulfur were used in place of the emission factors (EPA, 1995b). Given these findings, our confidence in the estimations of SO2 from cement kilns is low.

Example Calculations for Portland Cement Manufacturing

County-level portland and masonry cement production, which is difficult to obtain directly, is estimated by disaggregating statewide production to each county according to employment in the cement manufacturing industry. For each of California’s counties, the Census Bureau (2001) either reports exact employment or a range. If a range is given, the midpoint is used to quantify the proportion of statewide production assigned to a county.

Below are example calculations for Amador County for portland cement production. The Census Bureau (2001) reports that there are two portland cement processing facilities in Amador County with a total of 20 to 49 employees, the midpoint of which is equal to 34.5 employees (US Census Bureau, 2001). The number of employees per county is divided by the total number of employees for the state to derive the proportion of state production.

34.5 employees (Amador) ÷ 1,917.5 total employees (California) = 0.0180

This proportion is multiplied by the total state production to estimate the production of portland cement in Amador County.

29

0.0180 12,409,740 tons = 223,278 tons of cement produced (Amador)

The EPA estimates that roughly one-third of the raw materials processed through a cement kiln are lost to CO2 emissions. From this approximation, the consumption of raw materials can be calculated.

223,278 tons 3/2 = 335,000 tons of raw materials (Amador)

A second method to estimate the raw materials consumed is to calculate the ratio of California production to US production and multiply the ratio by US consumption of raw materials (USGS, 2001a).

130,819,000 metric tons (clinker) + 12,577,000 metric tons (cement) - 9,250,000 metric tons (finishing materials) = 134,146,000 metric tons (US consumption of raw materials in 1999)

134,146,000 1.05 growth=140,853,000 metric tons (US consumption of raw materials in 2000)

10,300,000 metric tons (California) ÷ 85,952,000 metric tons (US) = 0.12

0.12 140,853,000 metric tons (US) = 16,900,000 metric tons (California consumption of raw materials in 2000)

= 18,635,000 tons (California consumption of raw materials in 2000)

The proportion of material consumed in Amador County is estimated below and is equivalent to the initial estimate above.

0.0180 18,635,000 tons = 335,000 tons of raw materials (Amador)

Processes that produce particulate emissions include raw milling, the raw mill feed belt, air separating, and the weigh hopper. These are preparation steps for the kiln process. PM emissions are calculated by multiplying the estimated amount of raw materials processed by the corresponding emission factors (see Table 12).

335,000 tons (0.012 + 0.0031 + 0.032 + 0.019) = 22,300 pounds PM = 11 tons PM

PM emissions from the finish grinding mill and subsequent handling (including grinding, mill feed belt, air separator, and weigh hopper) are calculated similarly. However, the amount of material processed is considerably less than the initial raw material due to material loss in the kiln. Total clinker handled in the final milling stages is equal to total clinker produced plus imported clinker and added materials (gypsum or anhydrite). USGS (2001a) reports data for clinker imports, clinker production, and anhydrite use.

(10,645,000 metric tons of CA clinker + 0.12 4,607,000 metric tons of US imported clinker + 0.12 4,643,000 metric tons of US anhydrite) 2205

lb/metric ton ÷ 2000 lb/ton 1.05 growth30

= 13,600,000 tons (California final material processed in 2000)

0.0180 13,600,000 tons (California) = 244,800 tons (Amador)

PM emissions from finishing processes are calculated as the amount of finished material multiplied by the appropriate emission factors for grinding mill, mill feed belt, air separator, and weigh hopper.

244,800 tons (0.0080 + 0.0024 + 0.028 + 0.0094) ÷ 2000 = 5.9 tons PM

The emissions from the kiln process are more difficult to apportion to the state and county level. Four kiln processing techniques are used, which have different fuel consumption rates and chemical processes. Nationwide, the distribution of product by kiln processing methods is as follows: 27% wet, 22% long dry, 19% dry with preheater, and 32% dry with preheater/precalciner. However, in the state of California, there are no portland cement manufacturing facilities that employ the wet processing method. To roughly estimate the distribution of methods in California, the national distribution is normalized to account for 0% wet processing, as shown below.

22% long dry (US) ÷ (100-27)% = 30% long dry (California)

19% dry with a preheater (US) ÷ (100-27)% = 26% preheater (California)

32% dry with a preheater/precalciner (US) ÷ (100-27)% = 44% preheater/precalciner (California)

For Amador county, PM emissions from dry processing are estimated as the product of clinker production, the proportion of the production that follows the dry process, and the appropriate emission factor (see Table 12). USGS (2001a) reports that 11,736,000 tons of clinker were produced in California in 1999. With a 5% annual growth factor, it is estimated that year-2000 clinker production was 12,323,000 tons.

0.0180 12,323,000 tons (California) = 221,716 tons clinker produced (Amador)

221,716 tons clinker 30% 1.0 lb PM/ton ÷ 2000 = 33.3 tons PM from the long dry process (Amador)

The emissions from other types of kiln processes are estimated similarly. The dry process with preheater is estimated to generate 7.5 tons of PM and the dry process with preheater/precalciner is estimated to generate 10.2 tons PM.

Emissions from the clinker cooler are estimated as clinker production multiplied by the appropriate emission factor (Table 12).

221,716 tons clinker (Amador) 0.21 lb PM/ton ÷ 2000 = 23.3 tons PM

31

The total emissions for kiln processing are estimated as the sum total of PM emissions from the kiln processes plus emissions from the clinker cooler.

33.3 tons + 7.5 tons +10.2 tons + 23.3 tons = 74.3 tons PM

Total county-wide PM emissions from the production of portland cement are estimated as the sum of emissions from raw material processing, finish grinding, and kiln processes.

11 tons + 5.9 tons + 74.3 tons = 91.2 tons PM (Amador)

Table 13 lists the results of these calculations for all the counties that produce portland cement in the state of California.

Further example calculations are carried out to estimate emissions due to fuel combustion and chemical reactions for Amador County. The estimated amounts of clinker produced in Amador County by each of three dry processing methods (as calculated above) are multiplied by the appropriate emission factors from Table 11. The following example is the estimation of SO2

emissions from the long dry process of cement manufacturing. It is important to note that the emission factors for SO2 are not presented with high confidence and that the EPA (1995b) suggests a mass balance to estimate SO2 emissions, which requires site-specific data.

221,716 tons portland cement 30% 10 lb SO2/ton (1- 99.9% absorbance into product) ÷ 2000 = 0.33 tons SO2 (Amador)

The SO2 emissions from other kiln processing methods are calculated similarly. The dry process with preheater is estimated to generate 0.016 tons of SO2 and the dry process with preheater/precalciner is estimated to generate 0.054 tons of SO2 .

The total SO2 emissions in Amador County is the sum of the SO2 emissions from all kiln processes.

0.33 tons + 0.016 tons + 0.054 tons = 0.40 tons SO2 (Amador)

The emissions for the other criteria pollutants are calculated similarly. Table 14 shows the resultant emissions estimates for each county that produces portland cement.

32

Table 13. Annual PM emissions from cement manufacturing, including include raw material processing,kiln processing, and finish grinding.

County

Cou

nty

Prop

ortio

n of

St

ate

Empl

oym

ent

Tota

l Cem

ent

Prod

uctio

n by

C

ount

y (to

ns)

Tota

l Raw

M

ater

ials

C

onsu

med

(ton

s)

Raw

Mill

ing

Emis

sion

s(to

ns

PM)

Tota

l Clin

ker

Prod

uced

(ton

s)

Long

Dry

Kiln

Em

issi

ons (

tons

PM

)

Preh

eate

r Kiln

Em

issi

ons (

tons

PM

)

Preh

eate

r/ Pr

ecal

cine

r Kiln

Em

issi

ons (

tons

Clin

ker C

oole

r Em

issi

ons (

tons

PM

)

Qua

ntity

Of

Mat

eria

ls

Proc

esse

d In

Fi

nal S

tep

(tons

)

Grin

ding

Mill

Em

issi

ons (

tons

PM

)

Tota

l PM

Em

issi

ons (

tons

)

Amador 0.0180 223,278 335,100 11.08 221,716 33.26 7.49 10.24 23.28 244,836 5.85 91Kern 0.1638 2,032,156 3,049,894 100.80 2,017,938 302.69 68.21 93.23 211.88 2,228,363 53.26 830Lake 0.0021 25,887 38,852 1.28 25,706 3.86 0.87 1.19 2.70 28,387 0.68 11

Los Angeles 0.0188 232,986 349,669 11.56 231,356 34.70 7.82 10.69 24.29 255,481 6.11 95Mendocino 0.0010 12,944 19,426 0.64 12,853 1.93 0.43 0.59 1.35 14,193 0.34 5

Monterey 0.0355 440,085 660,487 21.83 437,006 65.55 14.77 20.19 45.89 482,575 11.53 180Orange 0.0010 12,944 19,426 0.64 12,853 1.93 0.43 0.59 1.35 14,193 0.34 5

Riverside 0.0389 482,152 723,621 23.92 478,778 71.82 16.18 22.12 50.27 528,704 12.64 197San

Bernardino0.4016 4,983,311 7,479,039 247.18 4,948,447 742.27 167.26 228.62 519.59 5,464,457 130.60 2,036

San Mateo 0.0180 223,278 335,100 11.08 221,716 33.26 7.49 10.24 23.28 244,836 5.85 91Santa Clara 0.1408 1,747,395 2,622,520 86.67 1,735,170 260.28 58.65 80.16 182.19 1,916,108 45.79 714Santa Cruz 0.0866 1,074,324 1,612,364 53.29 1,066,808 160.02 36.06 49.29 112.01 1,178,052 28.16 439

Shasta 0.0741 919,000 1,379,251 45.58 912,571 136.89 30.84 42.16 95.82 1,007,731 24.08 375Totals: 1 12,409,740 18,624,751 615.55 12,322,918 1,848 416.51 569.32 1,293 13,607,918 325.23 5,069

33

Table 14. Annual criteria pollutant emissions from kiln processing of cement.

County SO2 (tons)a NOX (tons) CO (tons) TOC (tons)Amador 0.40 543 216 12.0Kern 3.66 4,940 1,963 109.0Lake 0.05 63 25 1.4Los Angeles 0.42 566 225 12.5Mendocino 0.02 31 13 0.7Monterey 0.79 1,070 425 23.6Orange 0.02 31 13 0.7Riverside 0.87 1,172 466 25.9San Bernardino

8.97 12,114 4,814 267.2

San Mateo 0.40 543 216 12.0Santa Clara 3.15 4,248 1,688 93.7Santa Cruz 1.93 2,612 1,038 57.6Shasta 1.65 2,234 888 49.3Totals: 22.35 30,167 11,989 665.4

a Confidence is low in the emission factors and estimated emissions for SO2. EPA (1995b) recommends a mass balance on sulfur, which requires site-specific data.

34

Concrete Production Process Overview and Associated Emissions

Concrete is made by blending hydraulic cement powder (portland cement), water, sand and coarse aggregate. These components can be blended either in a truck in transit (“truck mixed”) or at the plant (“centrally mixed”). Nationwide, about 75% of concrete is truck mixed while the other 25 is centrally mixed (EPA, 2001). This ratio is assumed to be the same for California. The central-mix category includes shrink mixed concrete, which is partially mixed at the plant and continues to be mixed en route to the construction site.

At concrete mixing facilities, the raw material is purchased and stored on site. Sand and coarse aggregate are typically deposited in open storage piles until loaded by a truck onto a conveyor for transfer to elevated storage bins. Cement, however, is too fine to store in open areas and is stored in a storage silo. Cement is either transferred pneumatically or by a bucket elevator into the cement silo. From the elevated storage bins and the cement silo, the material is dropped into a weigh hopper, where the aggregate to cement ratio is proportioned correctly. The material is then either distributed to a mixing truck or a central mixer and water is added.

EPA (2001) provides emission factors for concrete production for several processes. Some fugitive emissions, namely storage pile and unpaved road dust emissions, were calculated using equations and parameters published by the EPA (1995a, 1998b). Table 15 lists PM and PM10 emissions factors for concrete production.

Table 15. PM and PM10 emission factors for concrete production(EPA, 2001; EPA, 1995a; EPA, 1998b).

Process PM (lb/ton material)a PM10 (lb/ ton material)Continuous drop: pile formation

NA 0.06

Batch drop 0.24 0.0024Aggregate transfer 0.029 NAStorage piles 0.00923 0.00436Cement unloading: pneumatic 0.27 NACement unloading: bucket elevator

0.24 NA

Weigh hopper loading 0.02 NACentral mix: mixer loading 0.04 NATruck mix: mixer loading 0.04 NATotal truck processing 0.1 NARoad dust 4.52 1.27a NA indicates “not available”. When emission factors for PM are not available the emission factors for PM10 are used.

35

In order to estimate the PM emission factor for vehicle traffic (and the associated emissions), EPA’s recommended method (EPA, 1998b) was adapted by employing the following assumptions: Silt content equals the EPA default value of 5.5% (EPA, 1998b). An average vehicle weight of 14 tons was assumed (based on an average truck capacity

of 8 yd3) (EPA, 2001). Moisture content of 2.1% is assumed from survey results of limestone product facilities

(EPA, 1995a). A typical facility is assumed to produce 60,000 tons/year of concrete, which must be

hauled by trucks. The typical truck traverses 0.1 mile of road on-site for each haul.

Activity Data

Yearly concrete production data is not reported by government agencies. However, cement is a primary component of concrete production. Therefore cement production can be used to roughly estimate concrete production. It is assumed that all portland cement ultimately is used for concrete manufacturing and masonry cement is not used for concrete manufacturing. To calculate the amount of concrete produced in the state of California, both in-state production and imports of portland cement and clinker must be considered. In 1999, California production of portland cement was 11,355,750 tons (USGS, 2001a). California total portland cement use totaled 12,720,000 tons in 1999, which includes imported cement and clinker (USGS, 2001a). EPA (2001) guidance suggests that a typical concrete blend is 12.5% cement by weight. Thus, the total concrete production for California can be estimated as follows.

12,720,000 tons cement ÷ 0.125 = 101,760,000 tons of concrete produced (California)

It is important to note that although the cement production industry experienced significant growth from 1999 to year 2000, the concrete manufacturing industry did not (California Employment Development Department, 2001). Therefore, the activity data reported for 1999 was not modified to include an industry growth factor and all emissions estimates are basis on 1999 activity data.

The US Census Bureau “County Business Patterns” database includes employment data for the concrete industry for California and its counties, which were used to disaggregate statewide production of concrete and estimate county-level productions (Census Bureau, 2001). To include all concrete production (not just production from ready-mix facilities), data were acquired for the broad Cement and Concrete Manufacturing Sector (NAICS 3273XX). The employment data from cement manufacturing was subtracted from the industry total to obtain only concrete manufacturing. This category includes ready-mix facilities and plants that manufacture concrete pipes, bricks, blocks, and other concrete products.

36

Temporal Allocation

Cement concrete production is weather dependent and emissions vary by time of year. A seasonal distribution is estimated from average rainfall (Western Regional Climate Center, 2001). A minimum monthly activity, 7% of the annual total, is assumed. The excess above the minimum is calculated from the normalized inverse of monthly rainfall. Thus, emissions decrease as rainfall increases. The recommended seasonal distribution is illustrated below.

January through March 21.8%April through June 25.7%July through September 29.7%October through December 22.7%

Diurnal variation varies by process type. In the concrete cement manufacturing industry, various production processes have different diurnal variations. The emissions from raw material storage piles are continuous: 24 hours a day, seven days a week. The remaining production processes for cement concrete (cement transfer, raw materials handling, and concrete mixing) are assigned a diurnal variation of a typical construction work week: 12 hours a day, seven days a week (Ghilotti Construction Co., pers. comm., 2001).

Additional Considerations

The EPA released revised emission factors for concrete batching process emissions after the emissions estimate for the CCOS project had been completed. These new emission factors and process changes can be used instead of the steps outlined below in the sample calculation (EPA, 2001).

Example Calculation for Concrete Manufacturing

County-level concrete production is estimated by disaggregating statewide production to each county. The statewide production is apportioned according to the county-by-county distribution of employment in the economic sector, Concrete Manufacturing. For each of California’s counties, the Census Bureau either reports an exact number of employees or a range. If a range is given, the midpoint is used to quantify the proportion of statewide production assigned to a county.

Below are example calculations for PM and criteria pollutant emissions for Butte County from concrete production. The Census Bureau (2001) reports that there are two concrete processing facilities in Butte County with a total of 40 to 99 employees, the midpoint of which is equal to 69.5 employees. The number of employees per county is divided by the total number of employees for the state to derive the proportion of state production.

69.5 employees (Butte) ÷ 18,270 total employees (California) = 0.0038

37

This proportion is multiplied by the total state production to estimate the production of concrete in Butte County.

0.0038 101,760,000 tons (California) = 387,110 tons of concrete produced (Butte)

The EPA based the emission factors on concrete composition of 12.5% by weight cement, 78.5% sand and coarse aggregate, and 9.0% water (EPA, 2001). From this ratio, the total consumption of raw materials used for concrete production can be roughly estimated for each county. The quantity of raw aggregates consumed in Butte county is estimated as follows:

387,110 tons concrete (Butte) 0.785 = 303,880 tons of raw aggregate consumed (Butte)

Handling of raw aggregates includes one continuous drop (pile formation), one truck batch drop, and a transfer to elevated bins. The PM emissions from concrete due to processing raw materials are calculated by multiplying the quantity of raw materials processed by the corresponding emission factors (see Table 14).

303,880 tons of raw aggregate (0.24 + 0.06 + 0.029) lb/ton ÷ 2000 = 50 tons PM(Butte)

PM emissions from wind erosion of storage piles for sand and aggregate are calculated similarly.

303,880 tons of raw aggregate 0.00923 lb/ton ÷ 2000 = 1.4 tons PM (Butte)

PM emissions from transferring cement into cement silos are estimated as the total amount of cement used multiplied by the emission factors for transfer processes (see Table 15). It is assumed that half of all concrete plants use a pneumatic transfer process and the other half employ bucket elevators.

387,110 tons concrete (Butte) 0.125 = 48,400 tons of cement (Butte)

48,400 tons (0.5 0.24 + 0.5 0.27) ÷ 2000 = 6.2 tons PM (Butte)

The next step in concrete production is the combination of dry materials in a weigh hopper. Loading dry materials into the weigh hopper is accomplished via gravity drop from elevated storage silos. PM emissions from this transfer are calculated by multiplying the loading emission factor from Table 15 by the weight of the dry material processed.

12.5% cement + 78.5% raw aggregates = 91% dry material

387,110 tons concrete 0.91 dry material = 48,400 tons of dry material

48,400 tons of dry material 0.02 lb/ton ÷ 2000 = 3.5 tons PM (Butte)

38

After the material is mixed and water is added, it is either deposited into a mixing truck or a mixer at the plant. On average, three-fourths of all concrete is truck mixed and the remainder is centrally mixed. The emissions that are generated by the central mixing process are calculated as follows.

0.25 387,110 tons concrete 0.04 lb/ton ÷ 2000 = 1.9 tons PM (Butte)

There are two different processes that generate emissions from truck-mixed concrete: mixing and handling processes. Emissions from mixing are calculated as follows.

0.75 387,110 tons concrete 0.04 lb/ton ÷ 2000 = 5.8 tons PM

Emissions from handling processes are calculated as follows.

0.75 387,110 tons concrete 0.1 lb/ton ÷ 2000 = 14.5 tons PM

The total emissions from truck-mixed and central-mixed concrete are the sum of emissions from all three emissions sources: central mixing, truck mixing, and truck processes.

1.9 tons + 5.8 tons + 14.5 tons = 22.2 tons PM (Butte)

To estimate fugitive emissions from vehicle traffic on unpaved roads, the number of vehicle miles traveled (VMT) at a typical facility were estimated. EPA (2001) defined a typical plant that produced around 30,000 yd3/year of concrete (the equivalent of 60,000 tons/year) and has an average road length of 0.1 miles. A typical truck load is 8 yd3. From these parameters it was calculated that for this facility, 1461 vehicle miles are traveled to pick up and drop off material (0.2 miles per round trip). This rate is equivalent to 0.024 miles/ton. Emissions are calculated as follows.

387,110 tons concrete produced (Butte) 0.024 mi/ton = 9,426 VMT (Butte)

9426 VMT 4.52 lb/VMT ÷ 2000 = 21.3 tons PM Total PM emissions from the production of concrete are estimated as the sum of emissions from raw material handling, transfer, and storage, plus emissions from mixing and road dust.

50 tons + 1.4 tons + 3.5 tons + 6.2 tons + 22.2 tons + 21.3 tons = 105 tons PM in Butte County

Table 16 lists the results of these equations for all the counties that produce concrete in the state of California.

39

Table 16. Annual PM emissions from concrete production per county.

County Propor-tion of State

Total Concrete Production by County (tons)

Aggre-gate

Trans-fers

(tons)

Cement Transfer

to Storage

Silo (tons)

Weigh Hopper Loading (tons)

Central Mix: Mixer

Loading (tons)

Truck Mix: Truck

Loading (tons)

Road Dust Emissions

(tons)

Wind Erosion

from Storage

Piles (tons)

Truck Mix:

Process (tons)

Total Emissions

(tons)

Alameda 0.0570 5,798,306 748.75 92.41 52.76 28.99 86.97 319.09 21.01 217.44 1,567.4Amador 0.0003 33,420 4.32 0.53 0.30 0.17 0.50 1.84 0.12 1.25 9.0

Butte 0.0038 387,111 49.99 6.17 3.52 1.94 5.81 21.30 1.40 14.52 104.6Calaveras 0.0019 192,163 24.81 3.06 1.75 0.96 2.88 10.57 0.70 7.21 51.9

Colusa 0.0004 38,990 5.03 0.62 0.35 0.19 0.58 2.15 0.14 1.46 10.5Contra Costa 0.0143 1,450,969 187.37 23.12 13.20 7.25 21.76 79.85 5.26 54.41 392.2

El Dorado 0.0022 220,013 28.41 3.51 2.00 1.10 3.30 12.11 0.80 8.25 59.5Fresno 0.0173 1,760,101 227.29 28.05 16.02 8.80 26.40 96.86 6.38 66.00 475.8Glenn 0.0030 306,347 39.56 4.88 2.79 1.53 4.60 16.86 1.11 11.49 82.8

Humboldt 0.0045 462,305 59.70 7.37 4.21 2.31 6.93 25.44 1.67 17.34 125.0Imperial 0.0096 971,954 125.51 15.49 8.84 4.86 14.58 53.49 3.52 36.45 262.7

Inyo 0.0008 80,764 10.43 1.29 0.73 0.40 1.21 4.44 0.29 3.03 21.8Kern 0.0481 4,895,976 632.23 78.03 44.55 24.48 73.44 269.43 17.74 183.60 1,323.5

Kings 0.0040 406,606 52.51 6.48 3.70 2.03 6.10 22.38 1.47 15.25 109.9Lake 0.0008 80,764 10.43 1.29 0.73 0.40 1.21 4.44 0.29 3.03 21.8

Lassen 0.0004 41,775 5.39 0.67 0.38 0.21 0.63 2.30 0.15 1.57 11.3Los Angeles 0.1268 12,899,979 1,665.81 205.59 117.39 64.50 193.50 709.90 46.73 483.75 3,487.2

Madera 0.0043 440,025 56.82 7.01 4.00 2.20 6.60 24.22 1.59 16.50 118.9Marin 0.0077 779,791 100.70 12.43 7.10 3.90 11.70 42.91 2.83 29.24 210.8

Mendocino 0.0004 41,775 5.39 0.67 0.38 0.21 0.63 2.30 0.15 1.57 11.3Merced 0.0096 971,954 125.51 15.49 8.84 4.86 14.58 53.49 3.52 36.45 262.7

Monterey 0.0024 239,507 30.93 3.82 2.18 1.20 3.59 13.18 0.87 8.98 64.7Napa 0.0395 4,015,926 518.59 64.00 36.54 20.08 60.24 221.00 14.55 150.60 1,085.6

Nevada 0.0045 456,735 58.98 7.28 4.16 2.28 6.85 25.13 1.65 17.13 123.5Orange 0.0543 5,525,379 713.51 88.06 50.28 27.63 82.88 304.07 20.02 207.20 1,493.6Placer 0.0096 971,954 125.51 15.49 8.84 4.86 14.58 53.49 3.52 36.45 262.7

Plumas 0.0010 105,829 13.67 1.69 0.96 0.53 1.59 5.82 0.38 3.97 28.6Riverside 0.0744 7,572,332 977.83 120.68 68.91 37.86 113.58 416.71 27.43 283.96 2,047.0

40

Table 16. Annual PM emissions from concrete production per county.

County Propor-tion of State

Total Concrete Production by County (tons)

Aggre-gate

Trans-fers

(tons)

Cement Transfer

to Storage

Silo (tons)

Weigh Hopper Loading (tons)

Central Mix: Mixer

Loading (tons)

Truck Mix: Truck

Loading (tons)

Road Dust Emissions

(tons)

Wind Erosion

from Storage

Piles (tons)

Truck Mix:

Process (tons)

Total Emissions

(tons)

Sacramento 0.0301 3,057,896 394.87 48.74 27.83 15.29 45.87 168.28 11.08 114.67 826.6San Benito 0.0118 1,203,107 155.36 19.17 10.95 6.02 18.05 66.21 4.36 45.12 325.2

San Bernardino

0.1541 15,679,378 2,024.72 249.89 142.68 78.40 235.19 862.85 56.80 587.98 4,238.5

San Diego 0.0504 5,129,914 662.44 81.76 46.68 25.65 76.95 282.30 18.58 192.37 1,386.7San

Francisco0.0099 1,002,589 129.47 15.98 9.12 5.01 15.04 55.17 3.63 37.60 271.0

San Joaquin 0.0295 3,002,197 387.68 47.85 27.32 15.01 45.03 165.21 10.88 112.58 811.6San Luis

Obispo0.0073 746,372 96.38 11.90 6.79 3.73 11.20 41.07 2.70 27.99 201.8

San Mateo 0.0189 1,918,844 247.79 30.58 17.46 9.59 28.78 105.60 6.95 71.96 518.7Santa

Barbara0.0096 971,954 125.51 15.49 8.84 4.86 14.58 53.49 3.52 36.45 262.7

Santa Clara 0.0540 5,491,960 709.19 87.53 49.98 27.46 82.38 302.23 19.90 205.95 1,484.6Santa Cruz 0.0028 284,067 36.68 4.53 2.59 1.42 4.26 15.63 1.03 10.65 76.8

Shasta 0.0078 790,931 102.13 12.61 7.20 3.95 11.86 43.53 2.87 29.66 213.8Siskiyou 0.0020 206,088 26.61 3.28 1.88 1.03 3.09 11.34 0.75 7.73 55.7

Solano 0.0257 2,612,301 337.33 41.63 23.77 13.06 39.18 143.76 9.46 97.96 706.2Sonoma 0.0176 1,793,520 231.60 28.58 16.32 8.97 26.90 98.70 6.50 67.26 484.8

Stanislaus 0.0085 863,341 111.49 13.76 7.86 4.32 12.95 47.51 3.13 32.38 233.4Tehama 0.0020 206,088 26.61 3.28 1.88 1.03 3.09 11.34 0.75 7.73 55.7Trinity 0.0001 11,140 1.44 0.18 0.10 0.06 0.17 0.61 0.04 0.42 3.0Tulare 0.0103 1,052,718 135.94 16.78 9.58 5.26 15.79 57.93 3.81 39.48 284.6

Tuolumne 0.0033 331,411 42.80 5.28 3.02 1.66 4.97 18.24 1.20 12.43 89.6Ventura 0.0172 1,754,531 226.57 27.96 15.97 8.77 26.32 96.55 6.36 65.79 474.3

Yolo 0.0205 2,085,942 269.36 33.24 18.98 10.43 31.29 114.79 7.56 78.22 563.9Yuba 0.0041 414,960 53.58 6.61 3.78 2.07 6.22 22.84 1.50 15.56 112.2

Totals 1 101,760,000 13,140 1,621 926 508 1,526 5,599 368 3,816 27,508

41

ASPHALTIC CONCRETE PRODUCTION

Asphaltic concrete primarily is used for paving and repairing road surfaces. Liquid asphalt cement is mixed with graded aggregate to produce asphaltic concrete. Liquid asphalt cement is a by-product of petroleum refining. It binds the aggregate together as it cools and hardens. Three types of asphalt concrete are used for road paving and maintenance: hot-mix asphalt (HMA), cutback asphalt, and emulsified asphalt. Cutback asphalt and emulsified asphalt represent only 3% and 7% of asphalt sales, respectively. However, cutback asphalt has a high VOC content and its use and production are associated with relatively high rates of VOC emissions.

Hot Mix Asphalt Process Overview and Associated Emissions

HMA predominantly is used to pave roads. Three HMA plant designs  batch mix, parallel-flow drum mix, and counterflow drum mix – employ different methods of mixing and heating to produce asphalt concrete. EPA (2000a) guidance for HMA production facilities documents the following process description for the three plant designs. At the beginning point of the production process, front-load trucks typically transfer aggregate material from storage piles to bins. Aggregate moves from the bins via conveyor belt to a rotary dryer and mixer. HMA plants use heat and dryers to reduce the moisture content of aggregate to near zero. In batch-mix plants, the hot aggregate is screened after drying to separate raw material into graded fractions. The graded aggregate is coated with asphalt binder and is segregated on the basis of size and weight in a weigh hopper. Batches of segregated aggregate are transferred to the mixer and dry mixed before the addition of pre-heated, pre-weighed liquid asphalt. Each batch of asphaltic concrete must be unloaded from the mixer before another batch can be produced. In drum-mix plants, aggregate is sized before it enters the rotary dryer. Subsequent mixing steps (coating, dry mixing, asphalt mixing) proceed continuously in a rotary dryer/drum mixer. Parallel-flow drum-mix plants blend materials in a dryer in which the dryer air stream moves unidirectionally with product flow. In addition, parallel-flow plants mix the raw materials the presence of hot dryer gases. In counterflow drum-mix plants, the dryer air stream moves countercurrent to the direction of product flow and mixing occurs after the liquid asphalt and aggregate pass beyond the heater. Because asphalt never directly contacts hot gases from the dryer, counterflow drum-mix plants may have relatively lower rates of VOC emissions than parallel-flow drum-mix plants. The final processing steps at HMA plants include transporting and loading the HMA product to hot storage silos or trucks via conveyor belt.

HMA plants are sources of PM, CO, NOx, SO2, VOC and TOC. PM and PM10 emissions arise from aggregate handling, storage, transportation, drying, mixing, and screening. CO, NOx, SO2, TOC, and VOC are by-products of fuel combustion processes. Additional TOC, VOC, and CO are emitted from heated asphalt cement during mixing process, post-production processes, and from asphalt storage tanks.

Table 17 lists EPA-recommended emission factors for fugitive PM sources. Collection devices capture process (or non-fugitive) PM and PM10 emissions, which arise from mixing,

42

drying, screening, and transferring aggregate within the plant. Captured particulate emissions are re-directed into the mixer and incorporated into the asphalt cement.

Process-associated emission factors for PM and other pollutants vary with plant design and/or fuel type (see Tables 18 and 19). EPA (2000a) suggests that 70% to 90% of plants use natural gas as fuel to power the dryers and mixers. Therefore, it is assumed that 80% of plants use natural gas and the remaining 20% use fuel oil or waste oil. The emissions from fuel combustion processes are incorporated with the “Industrial Natural Gas Combustion (Unspecified)” and “Industrial Distillate Oil Combustion” source categories, rather than the “Asphalt Cement” EIC category. In addition, EPA (2000a) suggests that batch-mix processes accounted for 48% of US production and drum-mix processes accounted for 52% of US production in 1996.

Table 20 lists emission factors for post-production handling activities, including silo filling, plant truck loading operations, and other post-production emissions. Open trucks that are loaded with HMA continue to emit TOC and CO from the HMA as the truck leaves the facility. The emission factors for these emissions are dependant upon the asphalt “loss-on heating” value. This is a measure of asphalt volatility, which varies by facility. For this memorandum, default loss-on heading values were used (EPA,2000a). Surveys would be required to treat this variable more thoroughly. The emission factor for PM emissions from Road dust on unpaved roads was estimated from EPA guidance (EPA, 1999b) by applying the following assumptions.

Silt content equals the EPA default value of 6.4% (EPA, 1998b). An average vehicle weight of 22 tons was assumed (EPA, 2000b). Moisture content equals 15% (EPA, 1995a or EPA, 2000b). 0.00114 vehicle miles are traveled (VMT) per ton product (EPA, 2000b). Vehicle speed equals 5 miles per hour (EPA, 2000b).

Table 21 tabulates estimated emission factors for losses of vapors from asphalt cement storage tanks. HMA plants use heated storage tanks to maintain an on-site stock of liquid asphalt cement, which is acquired from oil refineries, for use in the production process. The tanks are heated to keep the asphalt cement liquid. Emissions from heated asphalt storage tanks are best calculated by applying the TANKS software, as recommended by the EPA (EPA, 2000a), which requires site-specific data. Without plant-specific data, values for a reasonably typical plant (EPA, 2000b) were used to estimate emission factors for storage tanks (see Table 21). The underlying assumption is that a cylindrical storage tank with a length 50 ft, diameter 8 ft, and approximately one turnover a week is representative storage tanks at HMA plants. Emissions from the tank heater are not included in this inventory because fuel use data are unavailable. If site-specific or total fuel use data are available at a later time, AP-42 emission factors for fuel combustion may be applied (see AP-42, Chapter 1).

43

Table 17. PM and PM10 emission factors from aggregate storage, handling,and transport at HMA facilities (EPA, 1995a).

Process PM (lb/ton material)a, b PM10 (lb/ ton material)b

Continuous drop – pile formation NA 0.06Batch drop 0.24 0.0024Conveyor transfer NA 0.0014Storage piles 0.0056 0.0026a NA indicates data “not available”. When emission factors for PM are not available the emission factors for PM10

are used.b Note: units are pounds of pollutant per ton of aggregate, not product.

Table 18. PM and PM10 emission factors from HMA plant processes, including dryers, hot screens, and mixers (EPA, 2000a).

Process

Batch-mix Plant Drum-mix PlantPM (lb/ton product)a

PM10 (lb/ ton product)

PM (lb/ton product)a

PM10 (lb/ ton product)

Uncontrolled 32 4.5 28 6.5Venturi/fabric filter 0.14 0.027 0.045 0.023

. Emission factors for CO, NOx, SO2, TOC, and VOC from HMA plant processes,including dryers, hot screens, and mixers (EPA, 2000a).a

Plant Type Fuel Type

CO (lb/ton product)

NOx (lb/ton product)

SO2 (lb/ton product)

TOC (lb/ ton product)

VOC (lb/ ton product)

Batch Mix

Natural gas 0.40 0.025 0.0046 0.015 0.0082Fuel oil 0.40 0.12 0.088 0.015 0.0082Waste oil 0.40 0.12 0.088 NA

(assume 0.043)NA

(assume 0.036)Drum Mix

Natural gas 0.13 0.026 0.0034 0.044 0.032Fuel oil 0.13 0.055 0.011 0.044 0.032Waste oil 0.13 0.055 0.058 0.044 0.032

a The emissions from the rotary dryer are fuel combustion by-products and should be included in the “Industrial Natural Gas Combustion (Unspecified)” or “Industrial Distillate Fuel Combustion” EIC categories.

44

Table 20. Emission factors for PM, TOC, and CO from HMA plant post-production activities (EPA, 2000; EPA, 1999b).

ProcessPM

(lb/ton product)PM10

(lb/ton product)VOC a

(lb/ton product)CO

(lb/ton product)Silo filling 0.0006 NA 0.0122 0.0012Truck loading 0.0012 NA 0.0042 0.0014Open trucks NA NA 0.0011 0.00035Road dust 0.0011 0.00036 NA NAa Assume that TOC is equivalent to VOC

Table 21. Estimated emission factors for VOC and CO from asphalt cement storage tanks.

Process

VOC a

(lb/ton asphalt cement held in storage)

CO (lb/ton asphalt cement

held in storage)Asphalt cement storage tanks 0.02043 0.00198

a Assume that TOC is equivalent to VOC

Activity Data

The Energy Information Administration (EIA) of the US Department of Energy publishes total 1999 statewide productions of asphaltic cement and road oil (EIA, 2001). California state growth in the asphalt production industry was less than 5% from 1999 to 2000 (California Employment Development Department, 2001), therefore annual growth in production levels is negligible. Due to import and export of asphaltic cement between states, statewide production of asphalt cement and road oils may differ from statewide consumption by as much as 20% (EIA, 2001). However, consumption data are not available. Nationally, manufacturing of roofing supplies accounts for 20% of asphalt consumption, while asphalt concrete production accounts for the remainder (Tasker, 1996). Thus, the total amount of asphalt cement used for asphalt concrete is estimated to be 80% of asphaltic cement sales. Asphalt cement production was 20,366,000 barrels in California (EIA, 2001), which is equivalent to 3,943,000 tons of liquid asphalt cement. Of this amount, approximately 3,154,600 tons is used for asphalt concrete production.

The US Census Bureau “County Business Patterns” database includes employment data for the asphaltic concrete industry for California and its counties, which were used to disaggregate statewide production of asphalt concrete and estimate county-level productions (Census Bureau, 2001). Data were acquired for the Asphalt Paving Mixture and Block Manufacturing Sector (NAICS code 324121).

45

Temporal Allocation

Asphalt cement production is weather dependent and emissions vary by time of year. The seasonal that was presented for cement concrete production is recommended for use. The recommended seasonal distribution is illustrated below.

January through March 21.8%April through June 25.7%July through September 29.7%October through December 22.7%

Diurnal variation varies by process type. The emissions from raw material storage piles, and asphalt tank emissions are continuous (24 hours a day, seven days a week). The remaining production processes for asphalt cement production (raw materials handling, mixing, drying, and post-production processes) have the diurnal variation of a typical construction work week (12 hours a day, seven days a week) (Ghilotti Construction Co., pers. comm., 2001).

Additional Considerations

Due to cost efficiencies, HMA plant construction trends favor the counterflow drum-mix plant design over the batch-mix design by a ratio of 85 to 10 (EPA, 2000a). The counterflow drum-mix plant design facilitates use of more reclaimed asphalt pavement (RAP) in the production process than other plant designs. Research shows that counterflow plants can process as much as 50% RAP with little increase in emissions. Conversely, parallel-flow and batch-mix plants experience marked increases in VOC emissions when RAP is used (EPA,2000a).

Emissions for silo filling and truck loading operations increase with the temperature of the asphalt. Higher temperatures are used when the asphalt concrete is to be used for road paving in extreme weather conditions. Thus, plants located in counties with harsher climates would tend to have greater emissions than plants located in counties with mild climates.

Example Calculation for Asphaltic Concrete Production

It is estimated from available information (EIA, 2001; Tasker, 1996; EPA, 2000) that approximately 3,154,600 tons of asphalt cement is used for asphalt concrete production in California and that 90% of this is used for HMA production, 3% is used for cutback asphalt production, and 7% is used for emulsified asphalt production.

90% 3,154,600 tons of asphalt cement (California) = 2,839,200 tons of asphalt cement for HMA (California)

From the EPA AP-42 guidance document, the national production from batch-mix process versus drum-mix process was 48% and 52% of production, respectively, in 1996. However, the trend in the installation of new facilities has greatly favored the drum-mix production design

46

(approximately 90% of new plants are drum-mix plants) (EPA, 2000a). In California, there has been at least 10 new HMA facilities installed since 1996 (Census Bureau, 2001). If we assume the national trends in new HMA plants is consistent with California’s trends, then the relative production from batch-mix plants drops to 42% and production from drum-mix plants increases to 58%.

42% 2,839,200 tons of asphalt cement for HMA = 1,192,400 tons of asphalt cement for batch-mix processes (California)

58% 2,839,200 tons of asphalt cement for HMA = 1,646,700 tons of asphalt cement for drum-mix processes (California)

EPA (2000) states that asphalt concrete typically is comprised of 92% aggregate and 8% asphalt cement. Thus, the total production of asphalt concrete from batch-mix and drum-mix process are estimated as follows:

1,192,400 tons ÷ 0.08 = 14,905,500 tons of asphalt concrete produced by batch-mix plants

1,646,700 tons ÷ 0.08 = 20,583,800 tons of asphalt concrete produced by drum-mix plants

County-level asphalt concrete production is estimated by disaggregating statewide production to each county. The statewide production is apportioned according to the county-by-county distribution of employment in the economic sector, Asphalt Manufacturing, which the US Census Bureau identifies with the NAICS code no. 324121 (Asphalt Paving Mixture and Block Manufacturing). For each of California’s counties, the Census Bureau either reports an exact number of employees or a range (US Census Bureau, 2001). If a range is given, the midpoint is used to quantify the proportion of statewide production assigned to a county.

Batch-Mix Process Emissions

Below are example calculations for batch-mix asphalt concrete production in Alameda County. The Census Bureau (2001) reports that there are nine asphalt concrete processing facilities in Alameda County with a total of 55 to 99 employees, the midpoint of which is equal to 77 employees. The number of employees per county is divided by the total number of employees statewide to derive the proportion of state production.

77 employees (Alameda) ÷ 1,073 total employees (California) = 0.0718

This proportion is multiplied by the total state production to estimate the production of asphalt concrete by batch-mix plants in Alameda County.

0.0718 14,905,500 tons of asphalt (California) = 1,069,643 tons of asphalt produced (Alameda)

47

To appropriately estimate the emissions from various processes in the asphalt concrete industry, the mass of material handled for each process is needed. The emissions from handling raw aggregate prior to mixing are first calculated by estimating the total consumption of aggregates. The EPA (2000) suggests that asphalt concrete contains 92% by weight aggregate and 8% by weight asphalt cement. From this ratio, the total weight of the raw material consumed for asphalt concrete production can be estimated for each county.

0.92 1,069,643 tons (Alameda) = 984,072 tons aggregate consumed (Alameda)

The PM emissions from processing raw materials are calculated as the product of the estimated amount of raw materials processed and corresponding emission factors (see Table 17). Raw aggregate handling processes include one continuous drop, one truck batch drop, and a conveyor transfer to the rotary dryer.

984,072 tons aggregate (0.0014+0.24+0.06) lb/ ton aggregate ÷ 2000 = 148.3 tons of PM from aggregate handling

PM emissions from wind erosion of sand and aggregate storage piles are calculated similarly as follows.

984,072 tons aggregate 0.0056 lb/ ton aggregate ÷ 2000 = 2.76 tons PM from storage piles

PM emissions from the dryer are ducted to an emissions control device together with the emissions from hot screens, the weigh hopper, and mixing processes. Therefore, emission factors are selected with the assumption that control devices, such as a Venturi or wet scrubber are in place. These control devices capture less PM than fabric filters. Therefore, this estimation technique produces conservatively high emissions estimates.

1,069,643 tons product 0.14 lb/ton ÷ 2000 = 74.87 tons PM from ducted process emissions

After the asphalt is mixed thoroughly, it is either loaded into a truck for transportation to the construction site, or transported via conveyor to a storage silo. For conservatively high emissions calculation purposes, it is assumed that 100% of the HMA material is stored in a hot storage silo before it is loaded into a truck for transport. The emissions from silo filling and truck loading operations are calculated below.

1,069,643 tons product 0.0006 lb/ton product ÷ 2000 = 0.32 tons PM from silo filling

1,069,643 tons product 0.0012 lb/ton product ÷ 2000 = 0.64 tons PM from truck loading

Fugitive emissions from Road dust on unpaved roads are calculated as follows.

48

1,069,643 tons product 0.0011 lb/ton ÷ 2000 = 0.59 tons PM from unpaved roads Total PM emissions from the production of asphalt concrete is the sum of emissions from raw material handling, transfer, and storage, plus the ducted emissions from drying, and mixing, and the post-production fugitive emissions, including silo filing, truck loading, and Road dust on unpaved roads.

148.3 tons + 2.76 tons + 74.87 tons + 0.32 tons + 0.64 tons + 0.59 tons = 227.5 tons PM (Alameda)

Emissions of other criteria pollutants are calculated below. Fuel combustion emissions are estimated under the assumption that 80% of production is carried out at plants that use natural gas and 20% of production is carried out at plants that use fuel oil (EPA, 2000a). The emissions from these processes are calculated below by multiplying the quantity of HMA produced by the emission factors listed in Table 19. The emission factors are weighted by the estimated amount of each fuel type consumed. CO emissions are independent of fuel type.

1,069,643 tons product 0.4 lbs CO/ton ÷ 2000 = 213.9 tons CO

1,069,643 tons product (0.8 0.025 + 0.2 0.12) lbs NOx/ton ÷ 2000 = 23.5 tons NOx

1,069,643 tons product (0.8 0.0046 + 0.2 0.088) lbs SO2/ton ÷ 2000 = 11.4 tons SO2

1,069,643 tons product (0.8 0.015 + 0.2 0.043) lbs TOC/ton ÷ 2000 = 11.1 tons TOC

1,069,643 tons product (0.8 0.0082 + 0.2 0.036) lbs VOC/ton ÷ 2000 = 6.9 tons VOC

Additional VOC and CO emissions are generated by the volatilization of gases from the heated asphalt binder. These sources include emissions from the heated asphalt storage tank, fugitive emissions from silo filling and truck loading, and emissions from open transportation to the construction site. It is assumed that TOC from these volatilization processes is comprised mostly of heavier hydrocarbons, and all methane would be removed from asphalt cement binder in the refinement process. Thus TOC = VOC. The emission factors from these losses (see Table 20) are multiplied by total tons of asphalt produced, below.

1,069,643 tons product 0.0122 lbs VOC/ton ÷ 2000 = 6.52 tons VOC from silo filling

1,069,643 tons product 0.0042 lbs VOC/ton ÷ 2000 = 2.25 tons VOC from truck loading operations

1,069,643 tons product 0.0011 lbs VOC/ton ÷ 2000 = 0.59 tons VOC from open truck transport

Emissions from storage tank losses are calculated as the product of asphalt cement consumption and the emission factors shown in Table 21.

49

1,069,643 tons product 8% asphalt cement = 85,571 tons asphalt cement consumed (Alameda)

85,571 tons asphalt cement 0.0204 lbs VOC/ton ÷ 2000 = 0.87 tons VOC from storage tanks

Total VOC emissions are calculated by adding the VOC from fugitive emissions, storage tank losses, and production processes.

7.4 + 6.52 + 2.25 + 0.69 + .87 = 17.6 tons of VOC total

Similar calculations are carried out for CO emissions.

1,069,643 tons product 0.0012 lbs CO/ton ÷ 2000 = 0.64 tons CO from silo filling

1,069,643 tons product 0.0014 lbs CO /ton ÷ 2000 = 0.75 tons CO from truck loading operations

1,069,643 tons product 0.000352 lbs CO/ton ÷ 2000 = 0.19 tons CO from open truck transport

85,571 tons asphalt cement 0.00198 lbs CO/ton ÷ 2000 = 0.085 tons CO from storage tanks

0.64 + 0.75 + 0.19 + 0.085 + 213.9 = 215.6 tons CO total

Tables 22 through 26 tabulate emissions results for batch-mix process emissions for each county that produces asphalt concrete in the state of California.

Drum-Mix Process Emissions

The two different plant designs that utilize a drum-mix dryer are parallel flow and counterflow. The emissions differences between these two designs have not yet been identified. For the purposes of this example calculation, identical emission factors are applied for both plant designs.

The total amount of drum-mixed asphalt production for Alameda County is determined from the proportion of county to state-wide employment for asphalt concrete production.

0.0718 20,583,800 tons of asphalt concrete produced by drum-mix plants =1,477,126 tons of drum-mix asphalt concrete produced in Alameda county

To appropriately estimate the emissions from various processes in the asphalt concrete industry, the mass of material handled for each process is needed. The emissions from handling raw aggregate prior to mixing are first calculated by estimating the total amount of raw aggregates consumed. (Asphalt concrete is composed of 92% aggregate, by weight) (EPA, 2000a).

0.92 1,477,126 tons = 1,359,000 tons aggregate in Alameda County50

PM emissions from pre-production processing of raw materials are calculated in a manner similar to that for batch-mix applications.

1,359,000 tons aggregate (0.0014 + 0.24 + 0.06) lb/ton aggregate ÷ 2000 = 204.8 tons of PM from aggregate handling

1,359,000 tons aggregate 0.0056 lb/ton aggregate ÷ 2000 = 3.8 tons PM from storage piles

The PM emissions from the drum-mix dryer are ducted to an emissions control device and returned to the mixer. Therefore, emission factors are selected under the assumption that Venturi or wet scrubber control devices are in place.

1,477,126 tons product 0.045 lb/ton produced ÷ 2000 = 33.2 tons PM from the drum-mix dryer

After the asphalt is mixed thoroughly, it is either loaded into a truck for transportation to the construction site, or transported via conveyor to a storage silo. For conservatively high emissions calculation purposes, it is assumed that 100% of the HMA material is stored in a hot storage silo before it is loaded into a truck for transport.

1,477,126 tons product 0.0006 lb/ton produced ÷ 2000 = 0.44 tons PM from silo filling

1,477,126 tons product 0.0012 lb/ton produced ÷ 2000 = 0.89 tons PM from truck loading

Fugitive PM emissions from Road dust on unpaved roads are calculated in a similar manner to that for batch-mix plants.

1,477,126 tons product 0.0011 lb/ton produced ÷ 2000 = 0.81 tons PM from unpaved roads

Total PM emissions from the production of asphalt concrete at drum-mix plants are

estimated as the sum of emissions from raw material handling, transfer, and storage, plus the ducted emissions from drying and mixing, and post-production fugitive emissions (including silo filing, truck loading, and Road dust on unpaved roads).

204.8 tons + 3.8 tons + 33.2 tons + 0.44 tons + 0.89 tons + 0.84 tons = 244 tons PM (Alameda)

Emissions of other criteria pollutants are calculated below. The emissions from these processes are calculated below as the product of the quantity of HMA produced and the emission factors listed in Table 19. The emission factors are weighted according to the distribution of plant fuel used fuel type. (CO emissions are independent of fuel type.) It is assumed that 80% of production is carried out at plants that use natural gas, while 20% of production is carried out at plants that use fuel oil.

51

1,477,126 tons product 0.13 lbs CO/ton product ÷ 2000 = 96.0 tons CO

1,477,126 tons product (0.8 0.026 + 0.2 0.055) lbs NOx/ton product ÷ 2000 = 23.5 tons NOx

1,477,126 tons product (0.8 0.0034 + 0.2 0.011) lbs SO2/ton product ÷ 2000 = 3.6 tons SO2

1,477,126 tons product 0.044 lbs TOC/ton product ÷ 2000 = 32.5 tons TOC

1,477,126 tons product 0.032 lbs VOC/ton product ÷ 2000 = 23.6 tons VOC

VOC and CO emissions are generated from the volatilization of gases from asphalt storage tanks, during silo filling and truck loading, and during open truck transport from the plant. Example calculations for the fugitive emissions from these processes are provided in the previous section for batch-mix plants.

Tables 23 through 26 tabulate emissions results for drum-mix process emissions for each county that produces asphalt concrete in the state of California.

Cutback and Emulsified Asphalt Process Overview and Associated Emissions

Cutback and emulsified asphalts primarily are used for the preparation and maintenance of roads (Asphalt Institute, 2001). Production processes for cutback and emulsified asphalts differ from HMA production processes because the asphalt is not heated. Chemical additives, instead of heat, keep the asphalt in its liquid form. After application, these additives evaporate and the asphaltic concrete hardens and strengthens over time. Cutback asphalt additives (or diluents) are VOCs such as naphtha, gasoline, or kerosene (Texas Transportation Institute, 2001). Emulsified asphalt contains an emulsifying agent that improves mixing between the oily asphalt binder and water. Over time, the water and some of the emulsifying agent evaporates and the asphalt hardens. Emulsified asphalts are primarily used for surface treatments and spot repairs of roads. Cutback asphalt is used as a primer for the roadbed before the HMA is overlaid (Texas Transportation Institute, 2001). Cutback asphalt seals the aggregate road base and prevents moisture from degrading it, which would damage the asphalt concrete surface. A fine layer of cutback asphalt also acts to bind the road base and the HMA together.

Due to its large emissions rate, many counties in California have restricted the use of cutback asphalt (see Table 1, Attachment C to this memorandum). As a result of restrictions placed on use of cutback asphalt, the total amount of cutback asphalt produced in California is expected to be less than the national average, 3% of asphalt sales. Adjustments to county apportionment will be made to account for those counties with restrictions. In counties with

52

restrictions on cutback asphalt, the amount of cutback asphalt produced is assumed to be zero. However, for those counties without restricted use, the national average percent of cutback asphalt is applied to estimate the amount of cutback asphalt produced in each county. Currently, emulsified asphalt can be substituted for many uses of cutback asphalt. A larger ratio of emulsified asphalt to HMA is expected in counties that restrict cutback asphalt use. For the purposes of emissions estimation, it is assumed that emulsified asphalt is directly substituted for cutback asphalt in those counties with restrictions. Thus, emulsified asphalt production in counties that restrict cutback asphalt is equal to the national average use of emulsified asphalt plus cutback.

No emission factors are available from the EPA for cutback or emulsified asphalt production. However, emissions can be estimated on the basis of several assumptions. The VOC content of cutback asphalt is estimated to be an order of magnitude larger than that of emulsified asphalt and two orders of magnitude larger than HMA (EPA, 1994; EPA, 1995c). Therefore, the post-production TOC emissions due to volatilization are assumed to be two orders of magnitude larger for cutback cement than those from HMA production processes. Post-production emissions for emulsified asphalt are assumed to be one order of magnitude larger than those from HMA production processes. (As cutback and emulsified asphalts are not heated, this approach yields conservatively high VOC emissions estimates.) PM emissions from aggregate handling and storage in the cutback and emulsified asphalt production processes are similar to those for the HMA production process.

Example Calculation for Cutback and Emulsified Asphalt Production

Emissions due to handling and storage from cutback asphalt production in Alameda County are estimated below. Aggregate handling includes truck loading, conveyor transfer, and storage pile emissions. The aggregate is then dried and finely graded before being mixed with the cutback asphalt. Cutback asphalt represents about 3% of asphalt sales, nationally (EPA, 1995c). Alameda County is not subject to cutback asphalt restrictions, and therefore asphalt production in this case can be disaggregated according to national average distributions and county employment. Counties that restrict the use of cutback asphalt are assumed to substitute emulsified asphalt.

0.0718 3,154,600 tons of total asphalt cement (California)= 226,400 tons of asphalt cement used (Alameda)

3% for cutback 226,400 tons= 6,791 tons of asphalt cement used for cutback asphalt (Alameda)

6,791 tons asphalt ÷ 0.08 = 84,892 tons cutback asphalt concrete (Alameda)

84,892 tons cutback asphalt 0.92 aggregate = 78,100 tons aggregate used for cutback concrete (Alameda)

53

Example calculations for HMA illustrate emissions estimation for aggregate handling and storage. Emissions from drying aggregates and mixing cutback asphalt are estimated by applying emission factors for the batch-mix plant (Tables 18 and 19) to the total quantity of cutback asphalt produced in Alameda County. VOC emission factors for silo filling, truck loading operations, and open transportation to the construction site are estimated to be two orders of magnitude larger than those for HMA (i.e. multiply the VOC emission factors in Table 20 by 100). Because cutback asphalt is not heated, volatilization of CO is assumed to be negligible.

Total post-production VOC emission factor for batch-mix HMA = 0.0042 + 0.0122 + 0.0011 = 0.0175 lbs VOC/ton HMA

Total post-production VOC emission factor for cutback asphalt = 0.0175 100 = 1.75 lbs VOC/ton cutback asphalt

Because emulsified asphalt generally is not mixed with aggregate at the production plant, PM emissions from aggregate handling can be discounted. Also, because the aggregate is not dried or mixed with emulsified asphalt, there are no associated combustion emissions or PM emissions. Only VOC emissions from small contents of added organic solvents and transportation and storage losses are estimated. As stated previously, volatile emission factors are approximately one order of magnitude larger than those for HMA. Similar to cutback asphalt emissions, volatile emissions from emulsified asphalt are estimated by multiplying the HMA emission factors for VOC by a factor of 10 (see Table 20).

Total post-production VOC emission factor for emulsified asphalt = 0.0175 10 = 0.175 lbs VOC/ton emulsified asphalt

Emulsified asphalt, which accounts for about 7% of nationwide asphalt concrete sales, typically consists of no aggregates (at the time of sale) and 33% water (EPA, 1995c; Asphalt Institute, 2001). The remaining 66% is comprised of asphalt cement, emulsifier, and solvents. These factors are used to estimate the statewide and county-level productions of emulsified asphalt. (For counties that restrict the use of cutback asphalt, emulsified asphalt is assumed to be a substitute. Nationwide, cutback plus emulsified asphalt sales account for 10% of total asphalt concrete sales. For counties with no cutback sales, this factor is used to estimate sales of emulsified asphalt.)

0.0718 3,154,600 tons of asphalt cement (California)= 226,500 tons of asphalt cement used (Alameda)

7% 226,500 tons = 15,855 tons of asphalt cement used for emulsified asphalt (Alameda)

15,855 tons asphalt 0.33 = 48,000 tons of emulsified asphalt (Alameda)

54

Table 22. Annual PM emissions from batch-mix HMA facilities.

County Name

No. of Emp-loyees

(or range mid-point)

County% of State Production

County Asphalt

Production (tons)

Liquid Asphalt Cement (tons)

Aggre-gate

Handling (tons PM)

Storage Pile (tons

PM)

Dryer, Hot Screens, and

Mixer Venturi

Scrubber (tons PM)

Truck Loading

(tons PM)

Silo Filling (tons PM)

Un-paved Road (tons PM)

Total PM (tons PM)

Alameda 77 7.18% 1,069,643 85,571 148.30 2.76 74.87 0.64 0.32 0.59 227.48Contra Costa 7.5 0.70% 104,186 8,335 14.44 0.27 7.29 0.06 0.03 0.06 22.16

El Dorado 2 0.19% 27,783 2,223 3.85 0.07 1.94 0.02 0.01 0.02 5.91Fresno 30 2.80% 416,744 33,340 57.78 1.07 29.17 0.25 0.13 0.23 88.63

Inyo 25 2.33% 347,287 27,783 48.15 0.89 24.31 0.21 0.10 0.19 73.86Kern 25 2.33% 347,287 27,783 48.15 0.89 24.31 0.21 0.10 0.19 73.86Lake 2 0.19% 27,783 2,223 3.85 0.07 1.94 0.02 0.01 0.02 5.91

Lassen 9.5 0.89% 131,969 10,558 18.30 0.34 9.24 0.08 0.04 0.07 28.07Los Angeles 107 9.97% 1,486,387 118,911 206.08 3.83 104.05 0.89 0.45 0.82 316.11Mendocino 34.5 3.22% 479,256 38,340 66.45 1.23 33.55 0.29 0.14 0.26 101.92

Merced 4 0.37% 55,566 4,445 7.70 0.14 3.89 0.03 0.02 0.03 11.82Monterey 7 0.65% 97,240 7,779 13.48 0.25 6.81 0.06 0.03 0.05 20.68

Napa 14.5 1.35% 201,426 16,114 27.93 0.52 14.10 0.12 0.06 0.11 42.84Nevada 4 0.37% 55,566 4,445 7.70 0.14 3.89 0.03 0.02 0.03 11.82Orange 59.5 5.55% 826,542 66,123 114.60 2.13 57.86 0.50 0.25 0.45 175.78Placer 2 0.19% 27,783 2,223 3.85 0.07 1.94 0.02 0.01 0.02 5.91

Riverside 71 6.62% 986,294 78,904 136.74 2.54 69.04 0.59 0.30 0.54 209.76Sacramento 30 2.80% 416,744 33,340 57.78 1.07 29.17 0.25 0.13 0.23 88.63

San Bernardino 42 3.91% 583,442 46,675 80.89 1.50 40.84 0.35 0.18 0.32 124.08San Diego 72 6.71% 1,000,185 80,015 138.67 2.58 70.01 0.60 0.30 0.55 212.71

San Joaquin 4 0.37% 55,566 4,445 7.70 0.14 3.89 0.03 0.02 0.03 11.82San Luis Obispo 9.5 0.89% 131,969 10,558 18.30 0.34 9.24 0.08 0.04 0.07 28.07

San Mateo 47.5 4.43% 659,845 52,788 91.48 1.70 46.19 0.40 0.20 0.36 140.33Santa Barbara 9.5 0.89% 131,969 10,558 18.30 0.34 9.24 0.08 0.04 0.07 28.07

Santa Clara 174.5 16.26% 2,424,061 193,925 336.08 6.24 169.68 1.45 0.73 1.33 515.52Santa Cruz 4.5 0.42% 62,512 5,001 8.67 0.16 4.38 0.04 0.02 0.03 13.29

Shasta 174.5 16.26% 2,424,061 193,925 336.08 6.24 169.68 1.45 0.73 1.33 515.52Sonoma 4 0.37% 55,566 4,445 7.70 0.14 3.89 0.03 0.02 0.03 11.82

55

Table 22. Annual PM emissions from batch-mix HMA facilities.

County Name

No. of Emp-loyees

(or range mid-point)

County% of State Production

County Asphalt

Production (tons)

Liquid Asphalt Cement (tons)

Aggre-gate

Handling (tons PM)

Storage Pile (tons

PM)

Dryer, Hot Screens, and

Mixer Venturi

Scrubber (tons PM)

Truck Loading

(tons PM)

Silo Filling (tons PM)

Un-paved Road (tons PM)

Total PM (tons PM)

Stanislaus 2 0.19% 27,783 2,223 3.85 0.07 1.94 0.02 0.01 0.02 5.91Sutter 2 0.19% 27,783 2,223 3.85 0.07 1.94 0.02 0.01 0.02 5.91Tulare 9.5 0.89% 131,969 10,558 18.30 0.34 9.24 0.08 0.04 0.07 28.07

Ventura 4 0.37% 55,566 4,445 7.70 0.14 3.89 0.03 0.02 0.03 11.82Yolo 2 0.19% 27,783 2,223 3.85 0.07 1.94 0.02 0.01 0.02 5.91

Totals: 1073 100% 14,905,541 1,192,443 2,067 38.40 1,043 8.94 4.47 8.20 3,170

56

Table 23. Annual NOx, SO2, CO, TOC, and VOC emissions due to drying, screening, and mixing processes at HMA facilities.

County NameCounty % of

State Production

Batch-Mix Dryer, Hot Screens And Mixer Drum-Mix DryerNOx

(tons)SO2

(tons)CO

(tons)TOC(tons)

VOC (tons)

NOx

(tons)SO2

(tons)CO

(tons)TOC(tons)

VOC (tons)

Alameda 7.18% 23.53 11.38 213.93 11.12 6.9 23.49 3.63 96.01 32.50 23.63Contra Costa 0.70% 2.29 1.11 20.84 1.08 0.7 2.29 0.35 9.35 3.17 2.30

El Dorado 0.19% 0.61 0.30 5.56 0.29 0.2 0.61 0.09 2.49 0.84 0.61Fresno 2.80% 9.17 4.43 83.35 4.33 2.7 9.15 1.42 37.41 12.66 9.21

Inyo 2.33% 7.64 3.70 69.46 3.61 2.3 7.63 1.18 31.17 10.55 7.67Kern 2.33% 7.64 3.70 69.46 3.61 2.3 7.63 1.18 31.17 10.55 7.67Lake 0.19% 0.61 0.30 5.56 0.29 0.2 0.61 0.09 2.49 0.84 0.61

Lassen 0.89% 2.90 1.40 26.39 1.37 0.9 2.90 0.45 11.85 4.01 2.92Los Angeles 9.97% 32.70 15.82 297.28 15.46 9.6 32.64 5.05 133.42 45.16 32.84Mendocino 3.22% 10.54 5.10 95.85 4.98 3.1 10.52 1.63 43.02 14.56 10.59

Merced 0.37% 1.22 0.59 11.11 0.58 0.4 1.22 0.19 4.99 1.69 1.23Monterey 0.65% 2.14 1.03 19.45 1.01 0.6 2.14 0.33 8.73 2.95 2.15

Napa 1.35% 4.43 2.14 40.29 2.09 1.3 4.42 0.68 18.08 6.12 4.45Nevada 0.37% 1.22 0.59 11.11 0.58 0.4 1.22 0.19 4.99 1.69 1.23Orange 5.55% 18.18 8.79 165.31 8.60 5.4 18.15 2.81 74.19 25.11 18.26Placer 0.19% 0.61 0.30 5.56 0.29 0.2 0.61 0.09 2.49 0.84 0.61

Riverside 6.62% 21.70 10.49 197.26 10.26 6.4 21.66 3.35 88.53 29.96 21.79Sacramento 2.80% 9.17 4.43 83.35 4.33 2.7 9.15 1.42 37.41 12.66 9.21

San Bernardino 3.91% 12.84 6.21 116.69 6.07 3.8 12.81 1.98 52.37 17.73 12.89San Diego 6.71% 22.00 10.64 200.04 10.40 6.5 21.96 3.40 89.78 30.39 22.10

San Joaquin 0.37% 1.22 0.59 11.11 0.58 0.4 1.22 0.19 4.99 1.69 1.23San Luis

Obispo0.89% 2.90 1.40 26.39

1.37 0.92.90 0.45 11.85 4.01 2.92

San Mateo 4.43% 14.52 7.02 131.97 6.86 4.3 14.49 2.24 59.23 20.05 14.58Santa Barbara 0.89% 2.90 1.40 26.39 1.37 0.9 2.90 0.45 11.85 4.01 2.92

Santa Clara 16.26% 53.33 25.79 484.81 25.21 15.7 53.23 8.23 217.59 73.65 53.56Santa Cruz 0.42% 1.38 0.67 12.50 0.65 0.4 1.37 0.21 5.61 1.90 1.38

Shasta 16.26% 53.33 25.79 484.81 25.21 15.7 53.23 8.23 217.59 73.65 53.56Sonoma 0.37% 1.22 0.59 11.11 0.58 0.4 1.22 0.19 4.99 1.69 1.23

57

Table 23. Annual NOx, SO2, CO, TOC, and VOC emissions due to drying, screening, and mixing processes at HMA facilities.

County NameCounty % of

State Production

Batch-Mix Dryer, Hot Screens And Mixer Drum-Mix DryerNOx

(tons)SO2

(tons)CO

(tons)TOC(tons)

VOC (tons)

NOx

(tons)SO2

(tons)CO

(tons)TOC(tons)

VOC (tons)

Stanislaus 0.19% 0.61 0.30 5.56 0.29 0.2 0.61 0.09 2.49 0.84 0.61Sutter 0.19% 0.61 0.30 5.56 0.29 0.2 0.61 0.09 2.49 0.84 0.61Tulare 0.89% 2.90 1.40 26.39 1.37 0.9 2.90 0.45 11.85 4.01 2.92

Ventura 0.37% 1.22 0.59 11.11 0.58 0.4 1.22 0.19 4.99 1.69 1.23Yolo 0.19% 0.61 0.30 5.56 0.29 0.2 0.61 0.09 2.49 0.84 0.61

Totals: 100.00% 328 159 2,981 155 97 327 50.6 1,338 453 329a The emissions from the rotary dryer are fuel combustion by-products and the emissions should be apportioned to the “Industrial Natural Gas Combustion (Unspecified)” or “Industrial Distillate Oil Combustion” source categories.

58

Table 24. Annual volatile VOC and CO emissions from asphalt storage tanks, silo filling,truck loading operations, and HMA transportation for HMA facilities.

County Name

Asphalt Storage Tanks Volatile Emissions: Truck Loading

Volatile Emissions: Silo Filling

Open Truck Emissions

VOC (tons)

CO (tons)

VOC (tons)

CO (tons)

VOC (tons)

CO (tons)

VOC (tons)

CO (tons)

Alameda 2.078 0.202 5.35 1.783 15.54 1.528 1.401 0.448Contra Costa 0.202 0.020 0.52 0.174 1.51 0.149 0.136 0.044El Dorado 0.054 0.005 0.14 0.046 0.40 0.040 0.036 0.012Fresno 0.810 0.079 2.08 0.695 6.05 0.595 0.546 0.175Inyo 0.675 0.065 1.74 0.579 5.04 0.496 0.455 0.146Kern 0.675 0.065 1.74 0.579 5.04 0.496 0.455 0.146Lake 0.054 0.005 0.14 0.046 0.40 0.040 0.036 0.012Lassen 0.256 0.025 0.66 0.220 1.92 0.189 0.173 0.055Los Angeles 2.888 0.280 7.43 2.477 21.59 2.123 1.946 0.623Mendocino 0.931 0.090 2.40 0.799 6.96 0.685 0.628 0.201Merced 0.108 0.010 0.28 0.093 0.81 0.079 0.073 0.023Monterey 0.189 0.018 0.49 0.162 1.41 0.139 0.127 0.041Napa 0.391 0.038 1.01 0.336 2.93 0.288 0.264 0.084Nevada 0.108 0.010 0.28 0.093 0.81 0.079 0.073 0.023Orange 1.606 0.156 4.13 1.378 12.00 1.181 1.082 0.346Placer 0.054 0.005 0.14 0.046 0.40 0.040 0.036 0.012Riverside 1.916 0.186 4.93 1.644 14.32 1.409 1.292 0.413Sacramento 0.810 0.079 2.08 0.695 6.05 0.595 0.546 0.175San Bernardino 1.134 0.110 2.92 0.972 8.47 0.833 0.764 0.244San Diego 1.943 0.189 5.00 1.667 14.53 1.429 1.310 0.419San Joaquin 0.108 0.010 0.28 0.093 0.81 0.079 0.073 0.023San Luis Obispo 0.256 0.025 0.66 0.220 1.92 0.189 0.173 0.055San Mateo 1.282 0.124 3.30 1.100 9.58 0.943 0.864 0.277Santa Barbara 0.256 0.025 0.66 0.220 1.92 0.189 0.173 0.055Santa Clara 4.710 0.457 12.12 4.040 35.21 3.463 3.174 1.016

59

Table 24. Annual volatile VOC and CO emissions from asphalt storage tanks, silo filling,truck loading operations, and HMA transportation for HMA facilities.

County Name

Asphalt Storage Tanks Volatile Emissions: Truck Loading

Volatile Emissions: Silo Filling

Open Truck Emissions

VOC (tons)

CO (tons)

VOC (tons)

CO (tons)

VOC (tons)

CO (tons)

VOC (tons)

CO (tons)

Santa Cruz 0.121 0.012 0.31 0.104 0.91 0.089 0.082 0.026Shasta 4.710 0.457 12.12 4.040 35.21 3.463 3.174 1.016Sonoma 0.108 0.010 0.28 0.093 0.81 0.079 0.073 0.023Stanislaus 0.054 0.005 0.14 0.046 0.40 0.040 0.036 0.012Sutter 0.054 0.005 0.14 0.046 0.40 0.040 0.036 0.012Tulare 0.256 0.025 0.66 0.220 1.92 0.189 0.173 0.055Ventura 0.108 0.010 0.28 0.093 0.81 0.079 0.073 0.023Yolo 0.054 0.005 0.14 0.046 0.40 0.040 0.036 0.012Totals: 28.959 2.811 74.53 24.843 216.49 21.294 19.519 6.246

60

Table 25. Annual PM emissions from drum-mix HMA facilities.

County No.

of E

mpl

oyee

s (o

r ran

ge m

id-

poin

t)

Cou

nty

% o

f St

ate

Prod

uctio

n

Cou

nty

Asp

halt

Prod

uctio

n (to

ns)

Liqu

id A

spha

lt C

emen

t (to

ns)

Agg

rega

te

Han

dlin

g Em

issi

ons

(tons

PM

)

Stor

age

Pile

Em

issi

ons

(tons

PM

)

Dry

er, H

ot

Scre

ens,

and

Mix

er E

mis

sion

s (to

ns P

M)

Truc

k Lo

adin

g Em

issi

ons

(tons

PM

)

Silo

Fill

ing

Emis

sion

s (to

ns P

M)

Roa

d D

ust

Emis

sion

s (to

ns P

M)

Tota

l Em

issi

ons

(tons

PM

)

Alameda 77 7.18% 1,477,126 118,170 204.79 3.81 33.24 0.89 0.44 0.81 243.98Contra Costa 7.5 0.70% 143,876 11,510 19.95 0.37 3.24 0.09 0.04 0.08 23.76

El Dorado 2 0.19% 38,367 3,069 5.32 0.10 0.86 0.02 0.01 0.02 6.34Fresno 30 2.80% 575,504 46,040 79.79 1.48 12.95 0.35 0.17 0.32 95.06

Inyo 25 2.33% 479,586 38,367 66.49 1.24 10.79 0.29 0.14 0.26 79.21Kern 25 2.33% 479,586 38,367 66.49 1.24 10.79 0.29 0.14 0.26 79.21Lake 2 0.19% 38,367 3,069 5.32 0.10 0.86 0.02 0.01 0.02 6.34

Lassen 9.5 0.89% 182,243 14,579 25.27 0.47 4.10 0.11 0.05 0.10 30.10Los Angeles 107 9.97% 2,052,629 164,210 284.58 5.29 46.18 1.23 0.62 1.13 339.03Mendocino 34.5 3.22% 661,829 52,946 91.76 1.70 14.89 0.40 0.20 0.36 109.31

Merced 4 0.37% 76,734 6,139 10.64 0.20 1.73 0.05 0.02 0.04 12.67Monterey 7 0.65% 134,284 10,743 18.62 0.35 3.02 0.08 0.04 0.07 22.18

Napa 14.5 1.35% 278,160 22,253 38.57 0.72 6.26 0.17 0.08 0.15 45.94Nevada 4 0.37% 76,734 6,139 10.64 0.20 1.73 0.05 0.02 0.04 12.67Orange 59.5 5.55% 1,141,415 91,313 158.25 2.94 25.68 0.68 0.34 0.63 188.53Placer 2 0.19% 38,367 3,069 5.32 0.10 0.86 0.02 0.01 0.02 6.34

Riverside 71 6.62% 1,362,025 108,962 188.84 3.51 30.65 0.82 0.41 0.75 224.97Sacramento 30 2.80% 575,504 46,040 79.79 1.48 12.95 0.35 0.17 0.32 95.06

San Bernardino 42 3.91% 805,705 64,456 111.71 2.08 18.13 0.48 0.24 0.44 133.08San Diego 72 6.71% 1,381,208 110,497 191.50 3.56 31.08 0.83 0.41 0.76 228.13

San Joaquin 4 0.37% 76,734 6,139 10.64 0.20 1.73 0.05 0.02 0.04 12.67San Luis

Obispo9.5 0.89% 182,243 14,579 25.27 0.47 4.10 0.11 0.05 0.10 30.10

San Mateo 47.5 4.43% 911,214 72,897 126.33 2.35 20.50 0.55 0.27 0.50 150.51Santa Barbara 9.5 0.89% 182,243 14,579 25.27 0.47 4.10 0.11 0.05 0.10 30.10

61

Table 25. Annual PM emissions from drum-mix HMA facilities.

County No.

of E

mpl

oyee

s (o

r ran

ge m

id-

poin

t)

Cou

nty

% o

f St

ate

Prod

uctio

n

Cou

nty

Asp

halt

Prod

uctio

n (to

ns)

Liqu

id A

spha

lt C

emen

t (to

ns)

Agg

rega

te

Han

dlin

g Em

issi

ons

(tons

PM

)

Stor

age

Pile

Em

issi

ons

(tons

PM

)

Dry

er, H

ot

Scre

ens,

and

Mix

er E

mis

sion

s (to

ns P

M)

Truc

k Lo

adin

g Em

issi

ons

(tons

PM

)

Silo

Fill

ing

Emis

sion

s (to

ns P

M)

Roa

d D

ust

Emis

sion

s (to

ns P

M)

Tota

l Em

issi

ons

(tons

PM

)

Santa Clara 174.5 16.26% 3,347,512 267,801 464.11 8.62 75.32 2.01 1.00 1.84 552.91Santa Cruz 4.5 0.42% 86,326 6,906 11.97 0.22 1.94 0.05 0.03 0.05 14.26

Shasta 174.5 16.26% 3,347,512 267,801 464.11 8.62 75.32 2.01 1.00 1.84 552.91Sonoma 4 0.37% 76,734 6,139 10.64 0.20 1.73 0.05 0.02 0.04 12.67

Stanislaus 2 0.19% 38,367 3,069 5.32 0.10 0.86 0.02 0.01 0.02 6.34Sutter 2 0.19% 38,367 3,069 5.32 0.10 0.86 0.02 0.01 0.02 6.34Tulare 9.5 0.89% 182,243 14,579 25.27 0.47 4.10 0.11 0.05 0.10 30.10

Ventura 4 0.37% 76,734 6,139 10.64 0.20 1.73 0.05 0.02 0.04 12.67Yolo 2 0.19% 38,367 3,069 5.32 0.10 0.86 0.02 0.01 0.02 6.34

Totals: 1073 100% 20,583,843 1,646,707 2,854 53 463 12.4 6.2 11.3 3,400

62

Table 26. Sum of all annual emissions from hot mix asphalt, cutback and emulsified cement production processes.

County Name CO (tons) NOx (tons) SO2 (tons) TOC (tons) VOC (tons) PM (tons) PM10 (tons)Alameda 330.88 48.89 15.92 147.34 133.99 489.51 115.80Contra Costa 32.23 4.76 1.55 18.03 16.73 47.68 11.28El Dorado 8.15 1.22 0.39 3.32 2.99 12.25 2.91Fresno 122.30 18.32 5.85 49.87 44.79 183.68 43.62Inyo 107.43 15.87 5.17 60.12 55.78 158.93 37.60Kern 101.92 15.27 4.87 41.56 37.32 153.07 36.35Lake 8.59 1.27 0.41 4.81 4.46 12.71 3.01Lassen 40.82 6.03 1.96 22.84 21.20 60.39 14.29Los Angeles 459.80 67.93 22.12 257.29 238.75 680.23 160.91Mendocino 148.25 21.90 7.13 82.96 76.98 219.33 51.88Merced 16.31 2.44 0.78 6.65 5.97 24.49 5.82Monterey 28.54 4.27 1.36 11.64 10.45 42.86 10.18Napa 62.31 9.21 3.00 34.87 32.35 92.18 21.81Nevada 17.19 2.54 0.83 9.62 8.93 25.43 6.02Orange 255.68 37.78 12.30 143.08 132.76 378.26 89.48Placer 8.15 1.22 0.39 3.32 2.99 12.25 2.91Riverside 305.10 45.08 14.68 170.73 158.42 451.37 106.77Sacramento 122.30 18.32 5.85 49.87 44.79 183.68 43.62San Bernardino 171.22 25.65 8.19 69.82 62.70 257.16 61.07San Diego 293.52 43.97 14.04 119.70 107.49 440.84 104.70San Joaquin 16.31 2.44 0.78 6.65 5.97 24.49 5.82San Luis Obispo 38.73 5.80 1.85 15.79 14.18 58.17 13.81San Mateo 204.11 30.16 9.82 114.22 105.99 301.97 71.43Santa Barbara 38.73 5.80 1.85 15.79 14.18 58.17 13.81Santa Clara 749.85 110.79 36.07 419.61 389.36 1109.35 262.42Santa Cruz 18.34 2.75 0.88 7.48 6.72 27.55 6.54Shasta 711.38 106.55 34.03 290.10 260.51 1068.43 253.74Sonoma 17.19 2.54 0.83 9.62 8.93 25.43 6.02Stanislaus 8.15 1.22 0.39 3.32 2.99 12.25 2.91Sutter 8.59 1.27 0.41 4.81 4.46 12.71 3.01Tulare 38.73 5.80 1.85 15.79 14.18 58.17 13.81Ventura 16.31 2.44 0.78 6.65 5.97 24.49 5.82Yolo 8.15 1.22 0.39 3.32 2.99 12.25 2.91

63

Table 26. Sum of all annual emissions from hot mix asphalt, cutback and emulsified cement production processes.

County Name CO (tons) NOx (tons) SO2 (tons) TOC (tons) VOC (tons) PM (tons) PM10 (tons)Totals: 4,515 671 217 2,221 2,036 6,720 1,592

64

SURFACE BLASTING

Surface blasting is a large-scale industrial surface cleaning method. Industries that employ surface blasting include the aeronautic, automotive, container, non-ferrous metals, oil and gas, railway, ship building and repair, and steel industries. Abrasive material is propelled at high pressure to clean metal or concrete surfaces. The choice of abrasive depends on the surface type and the blasting conditions. Silica sand is the most commonly used abrasive, but coal slag, smelter slag, metallic abrasives, mineral abrasives, and synthetic abrasives are also used (EPA, 1998c). One factor that determines the choice of abrasive is the feasibility of reclaiming the abrasive material. Sand is relatively inexpensive and almost always is used when the material can not be reclaimed. Metallic, mineral, and synthetic abrasives are expensive and generally are used only when reclamation is possible.

Table 27 lists EPA-recommended PM emission factors for surface blasting with sand, which is the most commonly used abrasive. Emission rates depend upon wind speed (as shown in Table 27) and whether the abrasive material is wet or dry. Under wet blasting conditions, emission reductions of 50 to 93% have been observed (EPA, 1998c). For conservatively high emissions estimates, a 50% control efficiency for wet blasting may be assumed. It is important to note that wet blasting can only be used with abrasives that remain suspended in water, such as sand or glass beads (EPA, 1998c). If wind speeds are highly variable, the highest wind speed should be used to produce a conservatively high estimate.

Emission rates for other abrasives can be roughly approximated. Metallic grit abrasives generate PM emissions at a rate that is 76% lower than that of sand abrasives (EPA, 1998c). Metallic shot blasting emits 90% less PM than sand blasting (EPA, 1998c). Mineral abrasives are reported to produce significantly less dust than either sand or slag abrasives (EPA, 1998c), so it is conservatively assumed that mineral abrasives produce only 10% of the PM emissions that sand abrasives produce.

Table 27. PM emissions from sand blasting (EPA, 1998c).

Source Particle size and conditions

Emission factor: PM

(lb/1,000 lb abrasive)Sand Blasting of Mild Steel Panels

Total PM:5 mph wind speeds 2710 mph wind speeds 5515 mph wind speeds 91

PM10 13PM2.5 1.3

Abrasive Sand Blasting with Fabric Filter Control

Total PM 0.69

65

Activity Data

Quantities of materials produced and consumed in the US during the year 2000 for the end use “abrasive blasting” were acquired from the USGS (USGS, 2001c).

USGS estimated that 2,030,000 metric tons of coal combustion productsmostly boiler slagwere used mostly as blasting grit and to a lesser extent as roofing granules.

USGS estimated that 1,380,000 metric tons of industrial sand were used for abrasive blasting in the US.

USGS estimates that approximately 75% of metallic abrasives are used for blast cleaning. Based on USGS values and prices of consumed materials, we estimate that 200,000 metric tons of metallic abrasives were consumed in the US during the year 2000 for blast cleaning.

USGS estimated that 11,025 metric tons of garnet were used in the US as abrasive blasting media (or 45% of the year-2000 total apparent consumption of garnet, 24,500 tons). The most important users of garnet are the petroleum industry (for cleaning drill pipes and well casings), shipbuilding industry, aluminum aircraft industry, aluminum metals industry, and the structural steel fabrication industry. Garnet is slowly replacing silica as an abrasive blasting material due to health concerns about silica.

Manufactured abrasives that are used as for abrasive blasting include fused aluminum oxide, silicon carbide, and metallic abrasive (e.g., steel grit). Based on USGS values and prices of consumed materials, we estimate that approximately 160,000 metric tons of aluminum oxide and 340,000 metric tons of silicon carbide were used in the US during 2000. However, only an unknown portion of these materials were used as blasting abrasives.

In the year 2000, the percentages of US employment that are attributed to California for several industries that are known to employ abrasive blasting are as listed below (US Census Bureau, 2002).

Ship building and repair industry (NAICS 3366 ): 6% Aircraft manufacturing industry (NAICS 336411): 11% Steel product manufacturing industry (from purchased steel; NAICS 3312): 6% Alumina and aluminum production and processing industry (NAICS 3313): 5% Nonferrous (except aluminum) production and processing industry (NAICS 3314): 5% Fabricated metal product manufacturing industry (NAICS 332): 10% Oil and gas extraction industry (NAICS 211): 4%

On the basis of the employment fractions above, it is reasonable to assume that approximately 5% to 10% of the total US abrasive blasting materials consumption occurs in California. This assumption results in the following estimates of consumption for California:

101,000 to 203,000 metric tons of boiler slag 69,000 to 138,000 metric tons of industrial sand 10,000 to 20,000 metric tons of metallic abrasives 500 to 1,100 metric tons of garnet

66

Unknown fractions of up to 16,000 metric tons of aluminum oxide and up to 34,000 metric tons of silicon carbide

Statewide emissions estimates are computed as shown in Table 28. These estimates were produced by applying the emission factors shown in Table 27 with the assumptions that metallic abrasive emission factors are 76% lower and garnet emission factors are 90% lower than those of boiler slag or sand. Because these estimates are based on very crude assumptions and zero emissions controls, we consider them to be very rough and highly uncertain.

Table 28. Statewide consumptions of abrasive blasting materials and associated emissions for the State of California, year 2000.

Material

Year-2000 California Consumption

Emission Factors (lb/1,000 lb abrasive)

Year-2000 Emissions(tons per year)

metric tons tons 1,000 lb PM PM10 PM2.5 PM PM10 PM2.5

Boiler slag 203,000 224,000 448,000 30 13 1.3 6,700 2,900 290Sand 138,000 152,000 304,000 30 13 1.3 4,600 2,000 200Metallic abrasives 20,000 22,000 44,100 7 3.1 0.31 160 69 6.9

Garnet 1,100 1,200 2,400 3 1.3 0.13 4 2 0.2Totals 362,000 399,000 99,000 11,000 5,000 500All values are rounded to display only 2-3 significant figures.

Example Calculations for Surface Blasting

Hypothetical survey results are discussed below to facilitate an example calculation.

Facility no. 1 conducts about half of its blasting in an enclosed area. The other half is conducted with wet abrasive materials.

Facility no. 2 conducts about one-quarter of surface blasting in an enclosed area and performs the remainder using wetted abrasives.

Facility no. 3 conducts all surface blasting operations outdoors. Of this, about two-thirds of the operations proceed with wetted abrasives.

Table 28 lists the quantities of abrasives used.

67

Table 28. Quantities of abrasives used by type (hypothetical).

Abrasive Type Facility #1 (tons) Facility #2 (tons) Facility #3 (tons) Total (tons)Sand 900 1800 2,300 5,000Smelter slag 0 0 900 900Steel shot 0 250 0 250Aluminum oxide 600 0 0 600Glass beads 0 100 0 100Total 1,500 2,150 3,200 6,850

Sand and glass beads are the only abrasive materials (in this survey, at least) that will remain suspended in water and can be used when wetted. All other abrasive materials must be used dry. Steel shot, aluminum oxide, and glass beads are expensive and are most likely to be used in an enclosed area and reclaimed. Conversely, it can be assumed that sand is used predominately outdoors, where recovery is not feasible. From the numbers provided and ratio of wet and dry blasting, it is inferred that all sand was used in wet blasting conditions. For the emissions calculations presented below, assumptions are employed to produce conservatively high emissions estimates.

Emissions from sand blasting:5,000 tons wet sand 2 thousand lbs/ton = 10,000 thousand lbs abrasives

10,000 thousand lbs abrasive 50%(91) lb/thousand lbs ÷ 2000 = 227.5 tons PM from sand with wet controls

Emissions from slag:900 tons slag 2 thousand lbs/ton = 1,800 thousand lbs abrasives

1,800 thousand lbs abrasive (91) lb/thousand lbs ÷ 2000 = 81.9 tons PM from slag with no controls

Emissions from steel shot (enclosed area with fabric filter and recovery of material):250 tons wet sand 2 thousand lbs/ton = 500 thousand lbs abrasives

500 thousand lbs abrasive 0.69 lb/thousand lbs ÷ 2000 = 0.17 tons PM from steel shot with fabric filter control

Emissions from aluminum oxide (enclosed area with fabric filter and recovery of material):600 tons aluminum oxide 2 thousand lbs/ton = 1,200 thousand lbs abrasives

1,200 thousand lbs abrasive 0.69 lb/thousand lbs ÷ 2000 = 0.41 tons PM from Aluminum Oxide with fabric filter control

68

Emissions from Glass beads (wet controls and recovery of material):100 tons glass 2 thousand lbs/ton = 200 thousand lbs abrasives

200 thousand lbs abrasive 10%(91) lb/thousand lbs ÷ 2000 = 0.91 tons PM from glass with wet controls

Total PM= 227.5 +81.9 + 0.17+ 0.41+ 0.91 = 310.9 tons PM

PM10 emissions for uncontrolled blasting and wet blasting processes can be calculated in a similar manner by applying appropriate emission factors from Table 27.

69

REFERENCES

Asphalt Institute (2001) Asphalt in paving. Web site maintained by the Asphalt Institute, Lexington, Kentucky, and accessed August 2001 at web site http://www.asphaltinstitute.org/environ/is-186.html.

California Employment Development Department (2001) Employment by industry data. Database maintained by the California Employment Development Department, Sacramento, California, and accessed July 2001 at web site http://www.calmis.ca.gov/htmlfile/subject/indtable.htm.

EIA (2001) State energy data report – 1999. Report prepared by the EIA of the US Department of Energy, Washington, D.C. Published on the Internet at http://www.eia.doe.gov/emeu/sedr/contents.html.

Falasco, L. (2001) Personal communication. President of the Construction Materials Association. Sacramento, California. Telephone (209) 826-5955.

Hayden, J. (2001) Personal communication. Technical staff member of the National Stone, Sand, and Gravel Association. Arlington, Virginia. Telephone (800) 342-1415.

Lee C.H., Tang L.W.T., and Chang C.T. (2001) Modeling of fugitive dust emission for construction sand and gravel processing plant. Environ. Sci. Technol. 35, 10, 2073-2077.

National Stone Association (1995) Clean Air Management Guide. Published by the National Stone Association, Washington D.C.

Portland Cement Association (2001) Concrete basics. Web site maintained by the Portland Cement Association, Skokie, Illinois, and accessed July 2001 at web site http://www.portcement.org/cb/concretebasics_concretebasics.asp.

EPA (2001) Concrete batching. In compilation of air pollutant emission factors, vol. 1: stationary point and area emission units (AP-42), 5th ed. (January 1995), Supplement G (in process), Chapter 11.12. Report prepared by Office of Air Quality Planning and Standards of the EPA, Research Triangle Park, NC.

EPA (2000a) Hot mix asphalt plants. In compilation of air pollutant emission factors, vol. 1: stationary point and area emission units (AP-42), 5th ed. (January 1995), Supplement G (in process), Chapter 11.1. Report prepared by Office of Air Quality Planning and Standards of the EPA, Research Triangle Park, NC.

EPA (2000b) Emission factor documentation for AP-42 section 11.1, hot-mix asphalt production  final report, appendix B. Report prepared by Office of Air Quality Planning and Standards of the EPA, Research Triangle Park, NC.

70

EPA (1999a) Western surface coal mines. In compilation of air pollutant emission factors, vol. 1: stationary point and area emission units (AP-42), 5th ed. (January 1995), Supplement E (September 1999), Chapter 11.9. Report prepared by Office of Air Quality Planning and Standards of the EPA, Research Triangle Park, NC.

EPA (1999b) Unpaved Roads. In compilation of air pollutant emission factors, vol. 1: stationary point and area emission units (AP-42), 5th ed. (January 1995), Supplement E (September 1999), Chapter 13.2.2. Report prepared by Office of Air Quality Planning and Standards of the EPA, Research Triangle Park, NC.

EPA (1998a) Natural gas combustion. In compilation of air pollutant emission factors, vol. 1: stationary point and area emission units (AP-42), 5th ed. (January 1995), Supplement D (August 1998), Chapter 1.4. Report prepared by Office of Air Quality Planning and Standards of the EPA, Research Triangle Park, NC.

EPA (1998b) Paved Roads. In compilation of air pollutant emission factors, vol. 1: stationary point and area emission units (AP-42), 5th ed. (January 1995), Supplement D (August 1998), Chapter 13.2.1. Report prepared by Office of Air Quality Planning and Standards of the EPA, Research Triangle Park, NC.

EPA (1998c) Abrasive Blasting. In compilation of air pollutant emission factors, vol. 1: stationary point and area emission units (AP-42), 5th ed. (January 1995), Supplement D (August 1998), Chapter 13.2.6. Report prepared by Office of Air Quality Planning and Standards of the EPA, Research Triangle Park, NC.

EPA (1996) Sand and gravel processing. In compilation of air pollutant emission factors, vol. 1: stationary point and area emission units (AP-42), 5th ed. (January 1995), Supplement A (February 1996), Chapter 11.19. Report prepared by Office of Air Quality Planning and Standards of the EPA, Research Triangle Park, NC.

EPA (1995a) Aggregate handling and storage piles. In compilation of air pollutant emission factors, vol. 1: stationary point and area emission units (AP-42), 5th ed. (January 1995), Chapter 13.2.4. Report prepared by Office of Air Quality Planning and Standards of the EPA, Research Triangle Park, NC.

EPA (1995b) Portland cement manufacturing. In compilation of air pollutant emission factors, vol. 1: stationary point and area emission units (AP-42), 5th ed. (January 1995), Chapter 11.6. Report prepared by Office of Air Quality Planning and Standards of the EPA, Research Triangle Park, NC.

EPA (1995c) Asphalt paving operations. In compilation of air pollutant emission factors, vol. 1: stationary point and area emission units (AP-42), 5th ed. (January 1995), Chapter 4.5. Report prepared by Office of Air Quality Planning and Standards of the EPA, Research Triangle Park, NC.

EPA (1994). Final Report - Evaluation of Emissions from Paving Asphalts. U.S. Environmental Protection Agency, Office of Air Quality Planning and Standards, EPA-600/R-94-135. Research Triangle Park, North Carolina

71

Ghilotti Construction Company (2001). Personal communication on Nov. 26, 2001. Telephone (707) 585-1221.

Minin, Michael (2002). Employee of Lehigh Southwest Cement Co. in Redding, CA. Personal communication, September. Telephone (530) 275–1581.

Tasker, N.P. 1996. What do the cards hold for the asphalt industry? Presentation at the joint meeting of the International Slurry Surfacing Association and the Asphalt Emulsion Manufacturers Association, Phoenix, Arizona, February. http://www.srv.net/~whone/ia/iagen.html

Texas Transportation Institute (2001) Return on research: cleaner air from prime coat alternatives. Web site maintained by the Texas Transportation Institute’s Information and Technology Exchange Center, College Station, Texas, and accessed August 2001 at web site http://tti.tamu.edu/product/ror/primecoat.stm

US Census Bureau (2002) Censtats databases – county business patterns data. Database maintained by the US Census Bureau, Washington, D.C., and accessed August 2002 at web site http://tier2.census.gov/dbappweb.htm.

US Census Bureau (2001) Censtats databases – county business patterns data. Database maintained by the US Census Bureau, Washington, D.C., and accessed July 2001 at web site http://tier2.census.gov/dbappweb.htm.

USGS (2001a) Minerals yearbook1999, volume IIarea reports: domestic. Annual report prepared by the USGS of the US Department of the Interior, Washington, D.C. California chapter was prepared in cooperation with the Division of Mines and Geology of the California Department of Conservation. Published on the Internet at http://minerals.usgs.gov/minerals/pubs/commodity/myb/.

USGS (2001b) Mineral Industry Surveys. Report prepared by the USGS of the US Department of the Interior, Washington, D.C. Published on the Internet at http://minerals.usgs.gov/minerals/pubs/commodity/stone_crushed/63004400.pdf.

USGS (2001c) Minerals yearbook2000, volume 1metals and minerals. Chapter 4manufactured abrasives; chapter 20coal combustion products; chapter 31garnet; and chapter 68silica. Annual report prepared by the USGS of the US Department of the Interior, Washington, D.C. Published on the Internet at http://minerals.usgs.gov/minerals/pubs/commodity/myb/.

Western Regional Climate Center (2001) Historical Summaries. Database maintained by the Western Regional Climate Center, Reno, Nevada, and accessed October 2001 at web site http://www.wrcc.dri.edu/summary/climsmnca.html.

Young, C. (2001) Personal communication. Marketing/Quality Control Specialist with Stony Point Rock Quarry, Inc., Cotati, California. Telephone (707) 795-1775.

72

73